diff --git a/core/colours.js b/core/colours.js
index ea60b6ec8d..167336594b 100644
--- a/core/colours.js
+++ b/core/colours.js
@@ -17,109 +17,114 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+ import * as Blockly from 'blockly/core';
+
+ const cssColours = {
+   // SVG colours: these must be specificed in #RRGGBB style
+   // To add an opacity, this must be specified as a separate property (for SVG fill-opacity)
+   "motion": {
+     "primary": "#4C97FF",
+     "secondary": "#4280D7",
+     "tertiary": "#3373CC",
+     "quaternary": "#3373CC"
+   },
+   "looks": {
+     "primary": "#9966FF",
+     "secondary": "#855CD6",
+     "tertiary": "#774DCB",
+     "quaternary": "#774DCB"
+   },
+   "sounds": {
+     "primary": "#CF63CF",
+     "secondary": "#C94FC9",
+     "tertiary": "#BD42BD",
+     "quaternary": "#BD42BD"
+   },
+   "control": {
+     "primary": "#FFAB19",
+     "secondary": "#EC9C13",
+     "tertiary": "#CF8B17",
+     "quaternary": "#CF8B17"
+   },
+   "event": {
+     "primary": "#FFBF00",
+     "secondary": "#E6AC00",
+     "tertiary": "#CC9900",
+     "quaternary": "#CC9900"
+   },
+   "sensing": {
+     "primary": "#5CB1D6",
+     "secondary": "#47A8D1",
+     "tertiary": "#2E8EB8",
+     "quaternary": "#2E8EB8"
+   },
+   "pen": {
+     "primary": "#0fBD8C",
+     "secondary": "#0DA57A",
+     "tertiary": "#0B8E69",
+     "quaternary": "#0B8E69"
+   },
+   "operators": {
+     "primary": "#59C059",
+     "secondary": "#46B946",
+     "tertiary": "#389438",
+     "quaternary": "#389438"
+   },
+   "data": {
+     "primary": "#FF8C1A",
+     "secondary": "#FF8000",
+     "tertiary": "#DB6E00",
+     "quaternary": "#DB6E00"
+   },
+   // This is not a new category, but rather for differentiation
+   // between lists and scalar variables.
+   "data_lists": {
+     "primary": "#FF661A",
+     "secondary": "#FF5500",
+     "tertiary": "#E64D00",
+     "quaternary": "#E64D00"
+   },
+   "more": {
+     "primary": "#FF6680",
+     "secondary": "#FF4D6A",
+     "tertiary": "#FF3355",
+     "quaternary": "#FF3355"
+   },
+   "text": "#FFFFFF",
+   "workspace": "#F9F9F9",
+   "toolboxHover": "#4C97FF",
+   "toolboxSelected": "#e9eef2",
+   "toolboxText": "#575E75",
+   "toolbox": "#FFFFFF",
+   "flyout": "#F9F9F9",
+   "scrollbar": "#CECDCE",
+   "scrollbarHover": '#CECDCE',
+   "textField": "#FFFFFF",
+   "textFieldText": "#575E75",
+   "insertionMarker": "#000000",
+   "insertionMarkerOpacity": 0.2,
+   "dragShadowOpacity": 0.3,
+   "stackGlow": "#FFF200",
+   "stackGlowSize": 4,
+   "stackGlowOpacity": 1,
+   "replacementGlow": "#FFFFFF",
+   "replacementGlowSize": 2,
+   "replacementGlowOpacity": 1,
+   "colourPickerStroke": "#FFFFFF",
+   // CSS colours: support RGBA
+   "fieldShadow": "rgba(0,0,0,0.1)",
+   "dropDownShadow": "rgba(0, 0, 0, .3)",
+   "numPadBackground": "#547AB2",
+   "numPadBorder": "#435F91",
+   "numPadActiveBackground": "#435F91",
+   "numPadText": "white", // Do not use hex here, it cannot be inlined with data-uri SVG
+   "valueReportBackground": "#FFFFFF",
+   "valueReportBorder": "#AAAAAA",
+   "menuHover": "rgba(0, 0, 0, 0.2)",
+ };
 
 const Colours = {
-  // SVG colours: these must be specificed in #RRGGBB style
-  // To add an opacity, this must be specified as a separate property (for SVG fill-opacity)
-  "motion": {
-    "primary": "#4C97FF",
-    "secondary": "#4280D7",
-    "tertiary": "#3373CC",
-    "quaternary": "#3373CC"
-  },
-  "looks": {
-    "primary": "#9966FF",
-    "secondary": "#855CD6",
-    "tertiary": "#774DCB",
-    "quaternary": "#774DCB"
-  },
-  "sounds": {
-    "primary": "#CF63CF",
-    "secondary": "#C94FC9",
-    "tertiary": "#BD42BD",
-    "quaternary": "#BD42BD"
-  },
-  "control": {
-    "primary": "#FFAB19",
-    "secondary": "#EC9C13",
-    "tertiary": "#CF8B17",
-    "quaternary": "#CF8B17"
-  },
-  "event": {
-    "primary": "#FFBF00",
-    "secondary": "#E6AC00",
-    "tertiary": "#CC9900",
-    "quaternary": "#CC9900"
-  },
-  "sensing": {
-    "primary": "#5CB1D6",
-    "secondary": "#47A8D1",
-    "tertiary": "#2E8EB8",
-    "quaternary": "#2E8EB8"
-  },
-  "pen": {
-    "primary": "#0fBD8C",
-    "secondary": "#0DA57A",
-    "tertiary": "#0B8E69",
-    "quaternary": "#0B8E69"
-  },
-  "operators": {
-    "primary": "#59C059",
-    "secondary": "#46B946",
-    "tertiary": "#389438",
-    "quaternary": "#389438"
-  },
-  "data": {
-    "primary": "#FF8C1A",
-    "secondary": "#FF8000",
-    "tertiary": "#DB6E00",
-    "quaternary": "#DB6E00"
-  },
-  // This is not a new category, but rather for differentiation
-  // between lists and scalar variables.
-  "data_lists": {
-    "primary": "#FF661A",
-    "secondary": "#FF5500",
-    "tertiary": "#E64D00",
-    "quaternary": "#E64D00"
-  },
-  "more": {
-    "primary": "#FF6680",
-    "secondary": "#FF4D6A",
-    "tertiary": "#FF3355",
-    "quaternary": "#FF3355"
-  },
-  "text": "#FFFFFF",
-  "workspace": "#F9F9F9",
-  "toolboxHover": "#4C97FF",
-  "toolboxSelected": "#e9eef2",
-  "toolboxText": "#575E75",
-  "toolbox": "#FFFFFF",
-  "flyout": "#F9F9F9",
-  "scrollbar": "#CECDCE",
-  "scrollbarHover": '#CECDCE',
-  "textField": "#FFFFFF",
-  "textFieldText": "#575E75",
-  "insertionMarker": "#000000",
-  "insertionMarkerOpacity": 0.2,
-  "dragShadowOpacity": 0.3,
-  "stackGlow": "#FFF200",
-  "stackGlowSize": 4,
-  "stackGlowOpacity": 1,
-  "replacementGlow": "#FFFFFF",
-  "replacementGlowSize": 2,
-  "replacementGlowOpacity": 1,
-  "colourPickerStroke": "#FFFFFF",
-  // CSS colours: support RGBA
-  "fieldShadow": "rgba(0,0,0,0.1)",
-  "dropDownShadow": "rgba(0, 0, 0, .3)",
-  "numPadBackground": "#547AB2",
-  "numPadBorder": "#435F91",
-  "numPadActiveBackground": "#435F91",
-  "numPadText": "white", // Do not use hex here, it cannot be inlined with data-uri SVG
-  "valueReportBackground": "#FFFFFF",
-  "valueReportBorder": "#AAAAAA",
-  "menuHover": "rgba(0, 0, 0, 0.2)",
+  ...cssColours,
   overrideColours: function(colours) {
     // Colour overrides provided by the injection
     if (colours) {
@@ -148,4 +153,21 @@ const Colours = {
   }
 };
 
+function varify(coloursObj, prefix = '--colour') {
+  return Object.keys(coloursObj).map(key => {
+    const colour = coloursObj[key];
+    if (typeof colour === 'string') {
+      return `${prefix}-${key}: ${colour};`;
+    } else {
+      return varify(colour, `${prefix}-${key}`);
+    }
+  }).join('\n');
+}
+
+const cssVariables = `:root {
+  ${varify(cssColours)}
+}`;
+
+Blockly.Css.register(cssVariables);
+
 export {Colours};
diff --git a/core/css.js b/core/css.js
index 03c6bab0f1..f7b608451c 100644
--- a/core/css.js
+++ b/core/css.js
@@ -17,1007 +17,904 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+import * as Blockly from 'blockly/core';
+
+const styles = `
+  .blocklySvg {
+    background-color: var(--colour-workspace);
+    outline: none;
+    overflow: hidden;  /* IE overflows by default. */
+    position: absolute;
+    display: block;
+  }
 
-/**
- * @fileoverview Inject Blockly's CSS synchronously.
- * @author fraser@google.com (Neil Fraser)
- */
-'use strict';
-
-/**
- * @name Blockly.Css
- * @namespace
- */
-goog.provide('Blockly.Css');
-
-goog.require('Blockly.Colours');
+  /* Necessary to position the drag surface */
+  .blocklyRelativeWrapper {
+    position: relative;
+    width: 100%;
+    height: 100%;
+  }
 
-goog.require('goog.userAgent');
+  .blocklyWidgetDiv {
+    display: none;
+    position: absolute;
+    z-index: 99999; /* big value for bootstrap3 compatibility */
+  }
 
-/**
- * List of cursors.
- * @enum {string}
- */
-Blockly.Css.Cursor = {
-  OPEN: 'handopen',
-  CLOSED: 'handclosed',
-  DELETE: 'handdelete'
-};
+  .injectionDiv {
+    height: 100%;
+    position: relative;
+    overflow: hidden; /* So blocks in drag surface disappear at edges */
+    touch-action: none
+  }
 
-/**
- * Current cursor (cached value).
- * @type {string}
- * @private
- */
-Blockly.Css.currentCursor_ = '';
+  .blocklyNonSelectable {
+    user-select: none;
+    -moz-user-select: none;
+    -webkit-user-select: none;
+    -ms-user-select: none;
+  }
 
-/**
- * Large stylesheet added by Blockly.Css.inject.
- * @type {Element}
- * @private
- */
-Blockly.Css.styleSheet_ = null;
+  .blocklyWidgetDiv.fieldTextInput {
+    overflow: hidden;
+    border: 1px solid;
+    box-sizing: border-box;
+    transform-origin: 0 0;
+    -ms-transform-origin: 0 0;
+    -moz-transform-origin: 0 0;
+    -webkit-transform-origin: 0 0;
+  }
 
-/**
- * Path to media directory, with any trailing slash removed.
- * @type {string}
- * @private
- */
-Blockly.Css.mediaPath_ = '';
+  .blocklyWidgetDiv.fieldTextInput.removableTextInput {
+    overflow: visible;
+  }
 
-/**
- * Inject the CSS into the DOM.  This is preferable over using a regular CSS
- * file since:
- * a) It loads synchronously and doesn't force a redraw later.
- * b) It speeds up loading by not blocking on a separate HTTP transfer.
- * c) The CSS content may be made dynamic depending on init options.
- * @param {boolean} hasCss If false, don't inject CSS
- *     (providing CSS becomes the document's responsibility).
- * @param {string} pathToMedia Path from page to the Blockly media directory.
- */
-Blockly.Css.inject = function(hasCss, pathToMedia) {
-  // Clear the CSS if it has already been injected.
-  if (Blockly.Css.styleSheet_) {
-    document.head.removeChild(Blockly.Css.styleSheet_.ownerNode);
-  }
-  // Placeholder for cursor rule.  Must be first rule (index 0).
-  var text = '.blocklyDraggable {}\n';
-  if (hasCss) {
-    text += Blockly.Css.CONTENT.join('\n');
-    if (Blockly.FieldDate) {
-      text += Blockly.FieldDate.CSS.join('\n');
-    }
-  }
-  // Strip off any trailing slash (either Unix or Windows).
-  Blockly.Css.mediaPath_ = pathToMedia.replace(/[\\\/]$/, '');
-  text = text.replace(/<<<PATH>>>/g, Blockly.Css.mediaPath_);
-  // Dynamically replace colours in the CSS text, in case they have
-  // been set at run-time injection.
-  // Process longer colour properties first to handle common prefixes.
-  var compareByLength = function(a, b) { return b.length - a.length; };
-  var colourProperties = Object.keys(Blockly.Colours).sort(compareByLength);
-  for (var i = 0, colourProperty; colourProperty = colourProperties[i]; i++) {
-    // Replace all
-    text = text.replace(
-      new RegExp('\\$colour\\_' + colourProperty, 'g'),
-      Blockly.Colours[colourProperty]
-    );
-  }
-
-  // Inject CSS tag at start of head.
-  var cssNode = document.createElement('style');
-  document.head.insertBefore(cssNode, document.head.firstChild);
-
-  var cssTextNode = document.createTextNode(text);
-  cssNode.appendChild(cssTextNode);
-  Blockly.Css.styleSheet_ = cssNode.sheet;
-};
+  .blocklyTextDropDownArrow {
+    position: absolute;
+  }
 
-/**
- * Set the cursor to be displayed when over something draggable.
- * See See https://github.com/google/blockly/issues/981 for context.
- * @param {Blockly.Css.Cursor} cursor Enum.
- * @deprecated April 2017.
- */
-Blockly.Css.setCursor = function(cursor) {
-  console.warn('Deprecated call to Blockly.Css.setCursor.' +
-    'See https://github.com/google/blockly/issues/981 for context');
-};
+  .blocklyTextRemoveIcon {
+    position: absolute;
+    width: 24px;
+    height: 24px;
+    top: -40px;
+    left: 50%;
+    margin-left: -12px;
+    cursor: pointer;
+  }
 
-/**
- * Array making up the CSS content for Blockly.
- */
-Blockly.Css.CONTENT = [
-  '.blocklySvg {',
-    'background-color: $colour_workspace;',
-    'outline: none;',
-    'overflow: hidden;',  /* IE overflows by default. */
-    'position: absolute;',
-    'display: block;',
-  '}',
+  .blocklyNonSelectable {
+    user-select: none;
+    -moz-user-select: none;
+    -webkit-user-select: none;
+    -ms-user-select: none;
+  }
 
-  /* Necessary to position the drag surface */
-  '.blocklyRelativeWrapper {',
-    'position: relative;',
-    'width: 100%;',
-    'height: 100%;',
-  '}',
-
-  '.blocklyWidgetDiv {',
-    'display: none;',
-    'position: absolute;',
-    'z-index: 99999;', /* big value for bootstrap3 compatibility */
-  '}',
-
-  '.injectionDiv {',
-    'height: 100%;',
-    'position: relative;',
-    'overflow: hidden;', /* So blocks in drag surface disappear at edges */
-    'touch-action: none',
-  '}',
-
-  '.blocklyNonSelectable {',
-    'user-select: none;',
-    '-moz-user-select: none;',
-    '-webkit-user-select: none;',
-    '-ms-user-select: none;',
-  '}',
-
-  '.blocklyWidgetDiv.fieldTextInput {',
-    'overflow: hidden;',
-    'border: 1px solid;',
-    'box-sizing: border-box;',
-    'transform-origin: 0 0;',
-    '-ms-transform-origin: 0 0;',
-    '-moz-transform-origin: 0 0;',
-    '-webkit-transform-origin: 0 0;',
-  '}',
-
-  '.blocklyWidgetDiv.fieldTextInput.removableTextInput {',
-    'overflow: visible;',
-  '}',
-
-  '.blocklyTextDropDownArrow {',
-    'position: absolute;',
-  '}',
-
-  '.blocklyTextRemoveIcon {',
-    'position: absolute;',
-    'width: 24px;',
-    'height: 24px;',
-    'top: -40px;',
-    'left: 50%;',
-    'margin-left: -12px;',
-    'cursor: pointer;',
-  '}',
-
-  '.blocklyNonSelectable {',
-    'user-select: none;',
-    '-moz-user-select: none;',
-    '-webkit-user-select: none;',
-    '-ms-user-select: none;',
-  '}',
-
-  '.blocklyWsDragSurface {',
-    'display: none;',
-    'position: absolute;',
-    'top: 0;',
-    'left: 0;',
-  '}',
+  .blocklyWsDragSurface {
+    display: none;
+    position: absolute;
+    top: 0;
+    left: 0;
+  }
   /* Added as a separate rule with multiple classes to make it more specific
      than a bootstrap rule that selects svg:root. See issue #1275 for context.
   */
-  '.blocklyWsDragSurface.blocklyOverflowVisible {',
-    'overflow: visible;',
-  '}',
-
-  '.blocklyBlockDragSurface {',
-    'display: none;',
-    'position: absolute;',
-    'top: 0;',
-    'left: 0;',
-    'right: 0;',
-    'bottom: 0;',
-    'overflow: visible !important;',
-    'z-index: 50;', /* Display above the toolbox */
-  '}',
-
-  '.blocklyTooltipDiv {',
-    'background-color: #ffffc7;',
-    'border: 1px solid #ddc;',
-    'box-shadow: 4px 4px 20px 1px rgba(0,0,0,.15);',
-    'color: #000;',
-    'display: none;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 9pt;',
-    'opacity: 0.9;',
-    'padding: 2px;',
-    'position: absolute;',
-    'z-index: 100000;', /* big value for bootstrap3 compatibility */
-  '}',
-
-  '.blocklyDropDownDiv {',
-    'position: fixed;',
-    'left: 0;',
-    'top: 0;',
-    'z-index: 1000;',
-    'display: none;',
-    'border: 1px solid;',
-    'border-radius: 4px;',
-    'box-shadow: 0px 0px 8px 1px ' + Blockly.Colours.dropDownShadow + ';',
-    'padding: 4px;',
-    '-webkit-user-select: none;',
-    'min-height: 15px',
-  '}',
-
-  '.blocklyDropDownContent {',
-    'max-height: 300px;', // @todo: spec for maximum height.
-    'overflow: auto;',
-  '}',
-
-  '.blocklyDropDownArrow {',
-    'position: absolute;',
-    'left: 0;',
-    'top: 0;',
-    'width: 16px;',
-    'height: 16px;',
-    'z-index: -1;',
-    'background-color: inherit;',
-    'border-color: inherit;',
-  '}',
-
-  '.blocklyDropDownButton {',
-    'display: inline-block;',
-    'float: left;',
-    'padding: 0;',
-    'margin: 4px;',
-    'border-radius: 4px;',
-    'outline: none;',
-    'border: 1px solid;',
-    'transition: box-shadow .1s;',
-    'cursor: pointer;',
-  '}',
-
-  '.blocklyDropDownButtonHover {',
-    'box-shadow: 0px 0px 0px 4px ' + Blockly.Colours.fieldShadow + ';',
-  '}',
-
-  '.blocklyDropDownButton:active {',
-    'box-shadow: 0px 0px 0px 6px ' + Blockly.Colours.fieldShadow + ';',
-  '}',
-
-  '.blocklyDropDownButton > img {',
-    'width: 80%;',
-    'height: 80%;',
-    'margin-top: 5%',
-  '}',
-
-  '.blocklyDropDownPlaceholder {',
-    'display: inline-block;',
-    'float: left;',
-    'padding: 0;',
-    'margin: 4px;',
-  '}',
-
-  '.blocklyNumPadButton {',
-    'display: inline-block;',
-    'float: left;',
-    'padding: 0;',
-    'width: 48px;',
-    'height: 48px;',
-    'margin: 4px;',
-    'border-radius: 4px;',
-    'background: $colour_numPadBackground;',
-    'color: $colour_numPadText;',
-    'outline: none;',
-    'border: 1px solid $colour_numPadBorder;',
-    'cursor: pointer;',
-    'font-weight: 600;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 12pt;',
-    '-webkit-tap-highlight-color: rgba(0,0,0,0);',
-  '}',
-
-  '.blocklyNumPadButton > img {',
-    'margin-top: 10%;',
-    'width: 80%;',
-    'height: 80%;',
-  '}',
-
-  '.blocklyNumPadButton:active {',
-    'background: $colour_numPadActiveBackground;',
-    '-webkit-tap-highlight-color: rgba(0,0,0,0);',
-  '}',
-
-  '.arrowTop {',
-    'border-top: 1px solid;',
-    'border-left: 1px solid;',
-    'border-top-left-radius: 4px;',
-    'border-color: inherit;',
-  '}',
-
-  '.arrowBottom {',
-    'border-bottom: 1px solid;',
-    'border-right: 1px solid;',
-    'border-bottom-right-radius: 4px;',
-    'border-color: inherit;',
-  '}',
-
-  '.valueReportBox {',
-    'min-width: 50px;',
-    'max-width: 300px;',
-    'max-height: 200px;',
-    'overflow: auto;',
-    'word-wrap: break-word;',
-    'text-align: center;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: .8em;',
-  '}',
-
-  '.blocklyResizeSE {',
-    'cursor: se-resize;',
-    'fill: #aaa;',
-  '}',
-
-  '.blocklyResizeSW {',
-    'cursor: sw-resize;',
-    'fill: #aaa;',
-  '}',
-
-  '.blocklyResizeLine {',
-    'stroke: #888;',
-    'stroke-width: 1;',
-  '}',
-
-  '.blocklyHighlightedConnectionPath {',
-    'fill: none;',
-    'stroke: #fc3;',
-    'stroke-width: 4px;',
-  '}',
-
-  '.blocklyPath {',
-    'stroke-width: 1px;',
-  '}',
-
-  '.blocklySelected>.blocklyPath {',
-    // 'stroke: #fc3;',
-    // 'stroke-width: 3px;',
-  '}',
-
-  '.blocklySelected>.blocklyPathLight {',
-    'display: none;',
-  '}',
-
-  '.blocklyDraggable {',
+  .blocklyWsDragSurface.blocklyOverflowVisible {
+    overflow: visible;
+  }
+
+  .blocklyBlockDragSurface {
+    display: none;
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    overflow: visible !important;
+    z-index: 50; /* Display above the toolbox */
+  }
+
+  .blocklyTooltipDiv {
+    background-color: #ffffc7;
+    border: 1px solid #ddc;
+    box-shadow: 4px 4px 20px 1px rgba(0,0,0,.15);
+    color: #000;
+    display: none;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 9pt;
+    opacity: 0.9;
+    padding: 2px;
+    position: absolute;
+    z-index: 100000; /* big value for bootstrap3 compatibility */
+  }
+
+  .blocklyDropDownDiv {
+    position: fixed;
+    left: 0;
+    top: 0;
+    z-index: 1000;
+    display: none;
+    border: 1px solid;
+    border-radius: 4px;
+    box-shadow: 0px 0px 8px 1px var(--colour-dropDownShadow);
+    padding: 4px;
+    -webkit-user-select: none;
+    min-height: 15px
+  }
+
+  .blocklyDropDownContent {
+    max-height: 300px; // @todo: spec for maximum height.
+    overflow: auto;
+  }
+
+  .blocklyDropDownArrow {
+    position: absolute;
+    left: 0;
+    top: 0;
+    width: 16px;
+    height: 16px;
+    z-index: -1;
+    background-color: inherit;
+    border-color: inherit;
+  }
+
+  .blocklyDropDownButton {
+    display: inline-block;
+    float: left;
+    padding: 0;
+    margin: 4px;
+    border-radius: 4px;
+    outline: none;
+    border: 1px solid;
+    transition: box-shadow .1s;
+    cursor: pointer;
+  }
+
+  .blocklyDropDownButtonHover {
+    box-shadow: 0px 0px 0px 4px var(--colour-fieldShadow);
+  }
+
+  .blocklyDropDownButton:active {
+    box-shadow: 0px 0px 0px 6px var(--colour-fieldShadow);
+  }
+
+  .blocklyDropDownButton > img {
+    width: 80%;
+    height: 80%;
+    margin-top: 5%
+  }
+
+  .blocklyDropDownPlaceholder {
+    display: inline-block;
+    float: left;
+    padding: 0;
+    margin: 4px;
+  }
+
+  .blocklyNumPadButton {
+    display: inline-block;
+    float: left;
+    padding: 0;
+    width: 48px;
+    height: 48px;
+    margin: 4px;
+    border-radius: 4px;
+    background: var(--colour-numPadBackground);
+    color: var(--colour-numPadText);
+    outline: none;
+    border: 1px solid var(--colour-numPadBorder);
+    cursor: pointer;
+    font-weight: 600;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 12pt;
+    -webkit-tap-highlight-color: rgba(0,0,0,0);
+  }
+
+  .blocklyNumPadButton > img {
+    margin-top: 10%;
+    width: 80%;
+    height: 80%;
+  }
+
+  .blocklyNumPadButton:active {
+    background: var(--colour-numPadActiveBackground);
+    -webkit-tap-highlight-color: rgba(0,0,0,0);
+  }
+
+  .arrowTop {
+    border-top: 1px solid;
+    border-left: 1px solid;
+    border-top-left-radius: 4px;
+    border-color: inherit;
+  }
+
+  .arrowBottom {
+    border-bottom: 1px solid;
+    border-right: 1px solid;
+    border-bottom-right-radius: 4px;
+    border-color: inherit;
+  }
+
+  .valueReportBox {
+    min-width: 50px;
+    max-width: 300px;
+    max-height: 200px;
+    overflow: auto;
+    word-wrap: break-word;
+    text-align: center;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: .8em;
+  }
+
+  .blocklyResizeSE {
+    cursor: se-resize;
+    fill: #aaa;
+  }
+
+  .blocklyResizeSW {
+    cursor: sw-resize;
+    fill: #aaa;
+  }
+
+  .blocklyResizeLine {
+    stroke: #888;
+    stroke-width: 1;
+  }
+
+  .blocklyHighlightedConnectionPath {
+    fill: none;
+    stroke: #fc3;
+    stroke-width: 4px;
+  }
+
+  .blocklyPath {
+    stroke-width: 1px;
+  }
+
+  .blocklySelected>.blocklyPath {
+    // stroke: #fc3;
+    // stroke-width: 3px;
+  }
+
+  .blocklySelected>.blocklyPathLight {
+    display: none;
+  }
+
+  .blocklyDraggable {
     /* backup for browsers (e.g. IE11) that don't support grab */
-    'cursor: url("<<<PATH>>>/handopen.cur"), auto;',
-    'cursor: grab;',
-    'cursor: -webkit-grab;',
-    'cursor: -moz-grab;',
-  '}',
+    cursor: url("<<<PATH>>>/handopen.cur"), auto;
+    cursor: grab;
+    cursor: -webkit-grab;
+    cursor: -moz-grab;
+  }
 
-   '.blocklyDragging {',
+   .blocklyDragging {
     /* backup for browsers (e.g. IE11) that don't support grabbing */
-    'cursor: url("<<<PATH>>>/handclosed.cur"), auto;',
-    'cursor: grabbing;',
-    'cursor: -webkit-grabbing;',
-    'cursor: -moz-grabbing;',
-  '}',
+    cursor: url("<<<PATH>>>/handclosed.cur"), auto;
+    cursor: grabbing;
+    cursor: -webkit-grabbing;
+    cursor: -moz-grabbing;
+  }
   /* Changes cursor on mouse down. Not effective in Firefox because of
     https://bugzilla.mozilla.org/show_bug.cgi?id=771241 */
-  '.blocklyDraggable:active {',
+  .blocklyDraggable:active {
     /* backup for browsers (e.g. IE11) that don't support grabbing */
-    'cursor: url("<<<PATH>>>/handclosed.cur"), auto;',
-    'cursor: grabbing;',
-    'cursor: -webkit-grabbing;',
-    'cursor: -moz-grabbing;',
-  '}',
+    cursor: url("<<<PATH>>>/handclosed.cur"), auto;
+    cursor: grabbing;
+    cursor: -webkit-grabbing;
+    cursor: -moz-grabbing;
+  }
   /* Change the cursor on the whole drag surface in case the mouse gets
      ahead of block during a drag. This way the cursor is still a closed hand.
    */
-  '.blocklyBlockDragSurface .blocklyDraggable {',
+  .blocklyBlockDragSurface .blocklyDraggable {
     /* backup for browsers (e.g. IE11) that don't support grabbing */
-    'cursor: url("<<<PATH>>>/handclosed.cur"), auto;',
-    'cursor: grabbing;',
-    'cursor: -webkit-grabbing;',
-    'cursor: -moz-grabbing;',
-  '}',
-
-  '.blocklyDragging.blocklyDraggingDelete {',
-    'cursor: url("<<<PATH>>>/handdelete.cur"), auto;',
-  '}',
-
-  '.blocklyDragging.blocklyDraggingMouseThrough {',
-    'pointer-events: none;',
-  '}',
-
-  '.blocklyToolboxDelete {',
-    'cursor: url("<<<PATH>>>/handdelete.cur"), auto;',
-  '}',
-
-  '.blocklyToolboxGrab {',
-    'cursor: url("<<<PATH>>>/handclosed.cur"), auto;',
-    'cursor: grabbing;',
-    'cursor: -webkit-grabbing;',
-  '}',
-
-  '.blocklyDragging>.blocklyPath,',
-  '.blocklyDragging>.blocklyPathLight {',
-    'fill-opacity: 1.0;',
-    'stroke-opacity: 1.0;',
-  '}',
-
-  '.blocklyDragging>.blocklyPath {',
-  '}',
-
-  '.blocklyDisabled>.blocklyPath {',
-    'fill-opacity: .5;',
-    'stroke-opacity: .5;',
-  '}',
-
-  '.blocklyInsertionMarker>.blocklyPath {',
-    'stroke: none;',
-  '}',
-
-  '.blocklyText {',
-    'fill: $colour_text;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 12pt;',
-    'font-weight: 500;',
-  '}',
-
-  '.blocklyTextTruncated {',
-    'font-size: 11pt;',
-  '}',
-
-  '.blocklyNonEditableText>text {',
-    'pointer-events: none;',
-  '}',
-  '.blocklyNonEditableText>text,',
-  '.blocklyEditableText>text {',
-    'fill: $colour_textFieldText;',
-  '}',
-
-  '.blocklyEditableText>.blocklyEditableLabel {',
-    'fill: #fff;',
-  '}',
-
-  '.blocklyDropdownText {',
-    'fill: $colour_text !important;',
-  '}',
-
-  '.blocklyBubbleText {',
-    'fill: $colour_textFieldText;',
-  '}',
-  '.blocklyFlyout {',
-    'position: absolute;',
-    'z-index: 20;',
-  '}',
-  '.blocklyFlyoutButton {',
-    'fill: none;',
-    'pointer-events: all;',
-  '}',
-
-  '.blocklyFlyoutButtonBackground {',
-      'stroke: #c6c6c6;',
-  '}',
-
-  '.blocklyFlyoutButton .blocklyText {',
-    'fill: $colour_textFieldText;',
-  '}',
-
-  '.blocklyFlyoutButtonShadow {',
-    'fill: transparent;',
-  '}',
-
-  '.blocklyFlyoutButton:hover {',
-    'fill: white;',
-    'cursor: pointer;',
-  '}',
-
-  '.blocklyFlyoutLabel {',
-    'cursor: default;',
-  '}',
-
-  '.blocklyFlyoutLabelBackground {',
-    'opacity: 0;',
-  '}',
-
-  '.blocklyTouchTargetBackground {',
-    'fill: transparent;',
-    'cursor: pointer;',
-  '}',
-
-  '.blocklyFlyoutLabelText {',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 14pt;',
-    'fill: #575E75;',
-    'font-weight: bold;',
-  '}',
+    cursor: url("<<<PATH>>>/handclosed.cur"), auto;
+    cursor: grabbing;
+    cursor: -webkit-grabbing;
+    cursor: -moz-grabbing;
+  }
+
+  .blocklyDragging.blocklyDraggingDelete {
+    cursor: url("<<<PATH>>>/handdelete.cur"), auto;
+  }
+
+  .blocklyDragging.blocklyDraggingMouseThrough {
+    pointer-events: none;
+  }
+
+  .blocklyToolboxDelete {
+    cursor: url("<<<PATH>>>/handdelete.cur"), auto;
+  }
+
+  .blocklyToolboxGrab {
+    cursor: url("<<<PATH>>>/handclosed.cur"), auto;
+    cursor: grabbing;
+    cursor: -webkit-grabbing;
+  }
+
+  .blocklyDragging>.blocklyPath,
+  .blocklyDragging>.blocklyPathLight {
+    fill-opacity: 1.0;
+    stroke-opacity: 1.0;
+  }
+
+  .blocklyDragging>.blocklyPath {
+  }
+
+  .blocklyDisabled>.blocklyPath {
+    fill-opacity: .5;
+    stroke-opacity: .5;
+  }
+
+  .blocklyInsertionMarker>.blocklyPath {
+    stroke: none;
+  }
+
+  .blocklyText {
+    fill: var(--colour-text);
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 12pt;
+    font-weight: 500;
+  }
+
+  .blocklyTextTruncated {
+    font-size: 11pt;
+  }
+
+  .blocklyNonEditableText>text {
+    pointer-events: none;
+  }
+  .blocklyNonEditableText>text,
+  .blocklyEditableText>text {
+    fill: var(--colour-textFieldText);
+  }
+
+  .blocklyEditableText>.blocklyEditableLabel {
+    fill: #fff;
+  }
+
+  .blocklyDropdownText {
+    fill: $colour_text !important;
+  }
+
+  .blocklyBubbleText {
+    fill: var(--colour-textFieldText);
+  }
+  .blocklyFlyout {
+    position: absolute;
+    z-index: 20;
+  }
+  .blocklyFlyoutButton {
+    fill: none;
+    pointer-events: all;
+  }
+
+  .blocklyFlyoutButtonBackground {
+      stroke: #c6c6c6;
+  }
+
+  .blocklyFlyoutButton .blocklyText {
+    fill: var(--colour-textFieldText);
+  }
+
+  .blocklyFlyoutButtonShadow {
+    fill: transparent;
+  }
+
+  .blocklyFlyoutButton:hover {
+    fill: white;
+    cursor: pointer;
+  }
+
+  .blocklyFlyoutLabel {
+    cursor: default;
+  }
+
+  .blocklyFlyoutLabelBackground {
+    opacity: 0;
+  }
+
+  .blocklyTouchTargetBackground {
+    fill: transparent;
+    cursor: pointer;
+  }
+
+  .zelos-renderer.scratch-theme .blocklyFlyoutLabelText {
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 14pt;
+    fill: #575E75;
+    font-weight: bold;
+  }
 
   /*
     Don't allow users to select text.  It gets annoying when trying to
     drag a block and selected text moves instead.
   */
-  '.blocklySvg text, .blocklyBlockDragSurface text, .blocklyFlyout text, .blocklyToolboxDiv text {',
-    'user-select: none;',
-    '-moz-user-select: none;',
-    '-webkit-user-select: none;',
-    'cursor: inherit;',
-  '}',
-
-  '.blocklyHidden {',
-    'display: none;',
-  '}',
-
-  '.blocklyFieldDropdown:not(.blocklyHidden) {',
-    'display: block;',
-  '}',
-
-  '.blocklyIconGroup {',
-    'cursor: default;',
-  '}',
-
-  '.blocklyIconGroup:not(:hover),',
-  '.blocklyIconGroupReadonly {',
-    'opacity: .6;',
-  '}',
-
-  '.blocklyIconShape {',
-    'fill: #00f;',
-    'stroke: #fff;',
-    'stroke-width: 1px;',
-  '}',
-
-  '.blocklyIconSymbol {',
-    'fill: #fff;',
-  '}',
-
-  '.blocklyMinimalBody {',
-    'margin: 0;',
-    'padding: 0;',
-  '}',
-
-  '.blocklyCommentForeignObject {',
-    'position: relative;',
-    'z-index: 0;',
-  '}',
-
-  '.blocklyCommentRect {',
-    'fill: #E7DE8E;',
-    'stroke: #bcA903;',
-    'stroke-width: 1px',
-  '}',
-
-  '.blocklyCommentTarget {',
-    'fill: transparent;',
-    'stroke: #bcA903;',
-  '}',
-
-  '.blocklyCommentTargetFocused {',
-    'fill: none;',
-  '}',
-
-  '.blocklyCommentHandleTarget {',
-    'fill: none;',
-  '}',
-
-  '.blocklyCommentHandleTargetFocused {',
-    'fill: transparent;',
-  '}',
-
-  '.blocklyFocused>.blocklyCommentRect {',
-    'fill: #B9B272;',
-    'stroke: #B9B272;',
-  '}',
-
-  '.blocklySelected>.blocklyCommentTarget {',
-    'stroke: #fc3;',
-    'stroke-width: 3px;',
-  '}',
-
-
-  '.blocklyCommentTextarea {',
-    'background-color: #fef49c;',
-    'border: 0;',
-    'outline: 0;',
-    'margin: 0;',
-    'padding: 3px;',
-    'resize: none;',
-    'display: block;',
-    'overflow: hidden;',
-  '}',
-
-  '.blocklyCommentDeleteIcon {',
-    'cursor: pointer;',
-    'fill: #000;',
-    'display: none',
-  '}',
-
-  '.blocklySelected > .blocklyCommentDeleteIcon {',
-    'display: block',
-  '}',
-
-  '.blocklyDeleteIconShape {',
-    'fill: #000;',
-    'stroke: #000;',
-    'stroke-width: 1px;',
-  '}',
-
-  '.blocklyDeleteIconShape.blocklyDeleteIconHighlighted {',
-    'stroke: #fc3;',
-  '}',
+  .blocklySvg text, .blocklyBlockDragSurface text, .blocklyFlyout text, .blocklyToolboxDiv text {
+    user-select: none;
+    -moz-user-select: none;
+    -webkit-user-select: none;
+    cursor: inherit;
+  }
+
+  .blocklyHidden {
+    display: none;
+  }
+
+  .blocklyFieldDropdown:not(.blocklyHidden) {
+    display: block;
+  }
+
+  .blocklyIconGroup {
+    cursor: default;
+  }
+
+  .blocklyIconGroup:not(:hover),
+  .blocklyIconGroupReadonly {
+    opacity: .6;
+  }
+
+  .blocklyIconShape {
+    fill: #00f;
+    stroke: #fff;
+    stroke-width: 1px;
+  }
+
+  .blocklyIconSymbol {
+    fill: #fff;
+  }
+
+  .blocklyMinimalBody {
+    margin: 0;
+    padding: 0;
+  }
+
+  .blocklyCommentForeignObject {
+    position: relative;
+    z-index: 0;
+  }
+
+  .blocklyCommentRect {
+    fill: #E7DE8E;
+    stroke: #bcA903;
+    stroke-width: 1px
+  }
+
+  .blocklyCommentTarget {
+    fill: transparent;
+    stroke: #bcA903;
+  }
+
+  .blocklyCommentTargetFocused {
+    fill: none;
+  }
+
+  .blocklyCommentHandleTarget {
+    fill: none;
+  }
+
+  .blocklyCommentHandleTargetFocused {
+    fill: transparent;
+  }
+
+  .blocklyFocused>.blocklyCommentRect {
+    fill: #B9B272;
+    stroke: #B9B272;
+  }
+
+  .blocklySelected>.blocklyCommentTarget {
+    stroke: #fc3;
+    stroke-width: 3px;
+  }
+
+
+  .blocklyCommentTextarea {
+    background-color: #fef49c;
+    border: 0;
+    outline: 0;
+    margin: 0;
+    padding: 3px;
+    resize: none;
+    display: block;
+    overflow: hidden;
+  }
+
+  .blocklyCommentDeleteIcon {
+    cursor: pointer;
+    fill: #000;
+    display: none
+  }
+
+  .blocklySelected > .blocklyCommentDeleteIcon {
+    display: block
+  }
+
+  .blocklyDeleteIconShape {
+    fill: #000;
+    stroke: #000;
+    stroke-width: 1px;
+  }
+
+  .blocklyDeleteIconShape.blocklyDeleteIconHighlighted {
+    stroke: #fc3;
+  }
 
   // Scratch Comments
 
-  '.scratchCommentForeignObject {',
-    'position: relative;',
-  '}',
-
-  '.scratchCommentBody {',
-    'background-color: #fef49c;',
-    'border-radius: 4px;',
-  '}',
-
-  '.scratchCommentRect {',
-    'fill: #fef49c;',
-  '}',
-
-  '.scratchCommentTarget {',
-    'fill: transparent;',
-  '}',
-
-  '.scratchWorkspaceCommentBorder {',
-    'stroke: #bcA903;',
-    'stroke-width: 1px;',
-  '}',
-
-  '.scratchCommentTargetFocused {',
-    'fill: none;',
-  '}',
-
-  '.scratchCommentTopBar {',
-    'fill: #000000;',
-    'fill-opacity: 0.1',
-  '}',
-
-  '.scratchCommentText {',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 12pt;',
-    'font-weight: 400;',
-  '}',
-
-  '.scratchCommentTextarea {',
-    'background-color: #fef49c;',
-    'border: 0;',
-    'outline: 0;',
-    'padding: 0;',
-    'resize: none;',
-    'overflow: hidden;',
-  '}',
-
-  '.scratchCommentTextarea::placeholder {',
-    'color: rgba(0,0,0,0.5);',
-    'font-style: italic;',
-  '}',
-
-  '.scratchCommentResizeSE {',
-    'cursor: se-resize;',
-    'fill: transparent;',
-  '}',
-
-  '.scratchCommentResizeSW {',
-    'cursor: sw-resize;',
-    'fill: transparent;',
-  '}',
-
-  '.blocklyHtmlInput {',
-    'border: none;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 12pt;',
-    'height: 100%;',
-    'margin: 0;',
-    'outline: none;',
-    'box-sizing: border-box;',
-    'width: 100%;',
-    'text-align: center;',
-    'color: $colour_textFieldText;',
-    'font-weight: 500;',
-  '}',
-
-  '.blocklyMainBackground {',
-    'stroke-width: 1;',
-    'stroke: #c6c6c6;',  /* Equates to #ddd due to border being off-pixel. */
-  '}',
-
-  '.blocklyMutatorBackground {',
-    'fill: #fff;',
-    'stroke: #ddd;',
-    'stroke-width: 1;',
-  '}',
-
-  '.blocklyFlyoutBackground {',
-    'fill: $colour_flyout;',
-    'fill-opacity: .8;',
-  '}',
-
-  '.blocklyMainWorkspaceScrollbar {',
-    'z-index: 20;',
-  '}',
-
-  '.blocklyFlyoutScrollbar {',
-    'z-index: 30;',
-  '}',
-
-  '.blocklyScrollbarHorizontal, .blocklyScrollbarVertical {',
-    'position: absolute;',
-    'outline: none;',
-  '}',
-
-  '.blocklyScrollbarBackground {',
-    'opacity: 0;',
-  '}',
-
-  '.blocklyScrollbarHandle {',
-    'fill: $colour_scrollbar;',
-  '}',
-
-  '.blocklyScrollbarBackground:hover+.blocklyScrollbarHandle,',
-  '.blocklyScrollbarHandle:hover {',
-    'fill: $colour_scrollbarHover;',
-  '}',
-
-  '.blocklyZoom>image {',
-    'opacity: 1;',
-  '}',
+  .scratchCommentForeignObject {
+    position: relative;
+  }
+
+  .scratchCommentBody {
+    background-color: #fef49c;
+    border-radius: 4px;
+  }
+
+  .scratchCommentRect {
+    fill: #fef49c;
+  }
+
+  .scratchCommentTarget {
+    fill: transparent;
+  }
+
+  .scratchWorkspaceCommentBorder {
+    stroke: #bcA903;
+    stroke-width: 1px;
+  }
+
+  .scratchCommentTargetFocused {
+    fill: none;
+  }
+
+  .scratchCommentTopBar {
+    fill: #000000;
+    fill-opacity: 0.1
+  }
+
+  .scratchCommentText {
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 12pt;
+    font-weight: 400;
+  }
+
+  .scratchCommentTextarea {
+    background-color: #fef49c;
+    border: 0;
+    outline: 0;
+    padding: 0;
+    resize: none;
+    overflow: hidden;
+  }
+
+  .scratchCommentTextarea::placeholder {
+    color: rgba(0,0,0,0.5);
+    font-style: italic;
+  }
+
+  .scratchCommentResizeSE {
+    cursor: se-resize;
+    fill: transparent;
+  }
+
+  .scratchCommentResizeSW {
+    cursor: sw-resize;
+    fill: transparent;
+  }
+
+  .blocklyHtmlInput {
+    border: none;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 12pt;
+    height: 100%;
+    margin: 0;
+    outline: none;
+    box-sizing: border-box;
+    width: 100%;
+    text-align: center;
+    color: var(--colour-textFieldText);
+    font-weight: 500;
+  }
+
+  .blocklyMainBackground {
+    stroke-width: 1;
+    stroke: #c6c6c6;  /* Equates to #ddd due to border being off-pixel. */
+  }
+
+  .blocklyMutatorBackground {
+    fill: #fff;
+    stroke: #ddd;
+    stroke-width: 1;
+  }
+
+  .blocklyFlyoutBackground {
+    fill: var(--colour-flyout);
+    fill-opacity: .8;
+  }
+
+  .blocklyMainWorkspaceScrollbar {
+    z-index: 20;
+  }
+
+  .blocklyFlyoutScrollbar {
+    z-index: 30;
+  }
+
+  .blocklyScrollbarHorizontal, .blocklyScrollbarVertical {
+    position: absolute;
+    outline: none;
+  }
+
+  .blocklyScrollbarBackground {
+    opacity: 0;
+  }
+
+  .blocklyScrollbarHandle {
+    fill: var(--colour-scrollbar);
+  }
+
+  .blocklyScrollbarBackground:hover+.blocklyScrollbarHandle,
+  .blocklyScrollbarHandle:hover {
+    fill: var(--colour-scrollbarHover);
+  }
+
+  .blocklyZoom>image {
+    opacity: 1;
+  }
 
   /* Darken flyout scrollbars due to being on a grey background. */
   /* By contrast, workspace scrollbars are on a white background. */
-  '.blocklyFlyout .blocklyScrollbarHandle {',
-    'fill: #bbb;',
-  '}',
-
-  '.blocklyFlyout .blocklyScrollbarBackground:hover+.blocklyScrollbarHandle,',
-  '.blocklyFlyout .blocklyScrollbarHandle:hover {',
-    'fill: #aaa;',
-  '}',
-
-  '.blocklyInvalidInput {',
-    'background: #faa;',
-  '}',
-
-  '.blocklyAngleCircle {',
-    'stroke: ' + Blockly.Colours.motion.tertiary + ';',
-    'stroke-width: 1;',
-    'fill: ' + Blockly.Colours.motion.secondary + ';',
-  '}',
-
-  '.blocklyAngleCenterPoint {',
-    'stroke: #fff;',
-    'stroke-width: 1;',
-    'fill: #fff;',
-  '}',
-
-  '.blocklyAngleDragHandle {',
-    'stroke: #fff;',
-    'stroke-width: 5;',
-    'stroke-opacity: 0.25;',
-    'fill: #fff;',
-    'cursor: pointer;',
-  '}',
-
-  '.blocklyAngleDragArrow {',
-    'pointer-events: none',
-  '}',
-
-  '.blocklyAngleMarks {',
-    'stroke: #fff;',
-    'stroke-width: 1;',
-    'stroke-opacity: 0.5;',
-  '}',
-
-  '.blocklyAngleGauge {',
-    'fill: #fff;',
-    'fill-opacity: 0.20;',
-  '}',
-
-  '.blocklyAngleLine {',
-    'stroke: #fff;',
-    'stroke-width: 1;',
-    'stroke-linecap: round;',
-    'pointer-events: none;',
-  '}',
-
-  '.blocklyContextMenu {',
-    'border-radius: 4px;',
-    'max-height: 100%;',
-  '}',
-
-  '.blocklyDropdownMenu {',
-    'padding: 0 !important;',
-  '}',
-
-  '.blocklyDropDownNumPad {',
-    'background-color: $colour_numPadBackground;',
-  '}',
+  .blocklyFlyout .blocklyScrollbarHandle {
+    fill: #bbb;
+  }
+
+  .blocklyFlyout .blocklyScrollbarBackground:hover+.blocklyScrollbarHandle,
+  .blocklyFlyout .blocklyScrollbarHandle:hover {
+    fill: #aaa;
+  }
+
+  .blocklyInvalidInput {
+    background: #faa;
+  }
+
+  .blocklyAngleCircle {
+    stroke: var(--colour-motion-tertiary);
+    stroke-width: 1;
+    fill: var(--colour-motion-secondary);
+  }
+
+  .blocklyAngleCenterPoint {
+    stroke: #fff;
+    stroke-width: 1;
+    fill: #fff;
+  }
+
+  .blocklyAngleDragHandle {
+    stroke: #fff;
+    stroke-width: 5;
+    stroke-opacity: 0.25;
+    fill: #fff;
+    cursor: pointer;
+  }
+
+  .blocklyAngleDragArrow {
+    pointer-events: none
+  }
+
+  .blocklyAngleMarks {
+    stroke: #fff;
+    stroke-width: 1;
+    stroke-opacity: 0.5;
+  }
+
+  .blocklyAngleGauge {
+    fill: #fff;
+    fill-opacity: 0.20;
+  }
+
+  .blocklyAngleLine {
+    stroke: #fff;
+    stroke-width: 1;
+    stroke-linecap: round;
+    pointer-events: none;
+  }
+
+  .blocklyContextMenu {
+    border-radius: 4px;
+    max-height: 100%;
+  }
+
+  .blocklyDropdownMenu {
+    padding: 0 !important;
+  }
+
+  .blocklyDropDownNumPad {
+    background-color: var(--colour-numPadBackground);
+  }
 
   /* Override the default Closure URL. */
-  '.blocklyWidgetDiv .goog-option-selected .goog-menuitem-checkbox,',
-  '.blocklyWidgetDiv .goog-option-selected .goog-menuitem-icon {',
-    'background: url(<<<PATH>>>/sprites.png) no-repeat -48px -16px !important;',
-  '}',
+  .blocklyWidgetDiv .goog-option-selected .goog-menuitem-checkbox,
+  .blocklyWidgetDiv .goog-option-selected .goog-menuitem-icon {
+    background: url(<<<PATH>>>/sprites.png) no-repeat -48px -16px !important;
+  }
 
   /* Category tree in Toolbox. */
-  '.blocklyToolboxDiv {',
-    'background-color: $colour_toolbox;',
-    'color: $colour_toolboxText;',
-    'overflow-x: visible;',
-    'overflow-y: auto;',
-    'position: absolute;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'z-index: 40;', /* so blocks go over toolbox when dragging */
-    '-webkit-tap-highlight-color: transparent;', /* issue #1345 */
-  '}',
-
-  '.blocklyTreeRoot {',
-    'padding: 4px 0;',
-  '}',
-
-  '.blocklyTreeRoot:focus {',
-    'outline: none;',
-  '}',
-
-  '.blocklyTreeRow {',
-    'height: 22px;',
-    'line-height: 22px;',
-    'margin-bottom: 3px;',
-    'padding-right: 8px;',
-    'white-space: nowrap;',
-  '}',
-
-  '.blocklyHorizontalTree {',
-    'float: left;',
-    'margin: 1px 5px 8px 0;',
-  '}',
-
-  '.blocklyHorizontalTreeRtl {',
-    'float: right;',
-    'margin: 1px 0 8px 5px;',
-  '}',
-
-  '.blocklyToolboxDiv[dir="RTL"] .blocklyTreeRow {',
-    'margin-left: 8px;',
-  '}',
-
-  '.blocklyTreeRow:not(.blocklyTreeSelected):hover {',
-    'background-color: #e4e4e4;',
-  '}',
-
-  '.blocklyTreeSeparator {',
-    'border-bottom: solid #e5e5e5 1px;',
-    'height: 0;',
-    'margin: 5px 0;',
-  '}',
-
-  '.blocklyTreeSeparatorHorizontal {',
-    'border-right: solid #e5e5e5 1px;',
-    'width: 0;',
-    'padding: 5px 0;',
-    'margin: 0 5px;',
-  '}',
-
-  '.blocklyTreeIcon {',
-    'background-image: url(<<<PATH>>>/sprites.png);',
-    'height: 16px;',
-    'vertical-align: middle;',
-    'width: 16px;',
-  '}',
-
-  '.blocklyTreeIconClosedLtr {',
-    'background-position: -32px -1px;',
-  '}',
-
-  '.blocklyTreeIconClosedRtl {',
-    'background-position: 0px -1px;',
-  '}',
-
-  '.blocklyTreeIconOpen {',
-    'background-position: -16px -1px;',
-  '}',
-
-  '.blocklyTreeSelected>.blocklyTreeIconClosedLtr {',
-    'background-position: -32px -17px;',
-  '}',
-
-  '.blocklyTreeSelected>.blocklyTreeIconClosedRtl {',
-    'background-position: 0px -17px;',
-  '}',
-
-  '.blocklyTreeSelected>.blocklyTreeIconOpen {',
-    'background-position: -16px -17px;',
-  '}',
-
-  '.blocklyTreeIconNone,',
-  '.blocklyTreeSelected>.blocklyTreeIconNone {',
-    'background-position: -48px -1px;',
-  '}',
-
-  '.blocklyTreeLabel {',
-    'cursor: default;',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 16px;',
-    'padding: 0 3px;',
-    'vertical-align: middle;',
-  '}',
-
-  '.blocklyToolboxDelete .blocklyTreeLabel {',
-    'cursor: url("<<<PATH>>>/handdelete.cur"), auto;',
-  '}',
-
-  '.blocklyTreeSelected .blocklyTreeLabel {',
-    'color: #fff;',
-  '}',
-
-  '.blocklyDropDownDiv .goog-slider-horizontal {',
-    'margin: 8px;',
-    'height: 22px;',
-    'width: 150px;',
-    'position: relative;',
-    'outline: none;',
-    'border-radius: 11px;',
-    'margin-bottom: 20px;',
-  '}',
-
-  '.blocklyDropDownDiv .goog-slider-horizontal .goog-slider-thumb {',
-    'width: 26px;',
-    'height: 26px;',
-    'top: -1px;',
-    'position: absolute;',
-    'background-color: white;',
-    'border-radius: 100%;',
-    '-webkit-box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);',
-    '-moz-box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);',
-    'box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);',
-  '}',
-
-  '.scratchEyedropper {',
-    'background: none;',
-    'outline: none;',
-    'border: none;',
-    'width: 100%;',
-    'text-align: center;',
-    'border-top: 1px solid #ddd;',
-    'padding-top: 5px;',
-    'cursor: pointer;',
-  '}',
-
-  '.scratchColourPickerLabel {',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 0.65rem;',
-    'color: $colour_toolboxText;',
-    'margin: 8px;',
-  '}',
-
-  '.scratchColourPickerLabelText {',
-    'font-weight: bold;',
-  '}',
-
-  '.scratchColourPickerReadout {',
-    'margin-left: 10px;',
-  '}',
-
-  '.scratchMatrixButtonDiv {',
-    'width: 50%;',
-    'text-align: center;',
-    'float: left;',
-  '}',
-
-  '.scratchNotePickerKeyLabel {',
-    'font-family: "Helvetica Neue", Helvetica, sans-serif;',
-    'font-size: 0.75rem;',
-    'fill: $colour_textFieldText;',
-    'pointer-events: none;',
-  '}',
+  .blocklyToolboxDiv {
+    background-color: var(--colour-toolbox);
+    color: var(--colour-toolboxText);
+    overflow-x: visible;
+    overflow-y: auto;
+    position: absolute;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    z-index: 40; /* so blocks go over toolbox when dragging */
+    -webkit-tap-highlight-color: transparent; /* issue #1345 */
+    padding: 0;
+  }
+
+  .blocklyTreeRoot {
+    padding: 4px 0;
+  }
+
+  .blocklyTreeRoot:focus {
+    outline: none;
+  }
+
+  .blocklyTreeRow {
+    line-height: 22px;
+    margin: 0;
+    padding: 0.375rem 0px;
+    white-space: nowrap;
+    cursor: pointer;
+  }
+
+  .blocklyHorizontalTree {
+    float: left;
+    margin: 1px 5px 8px 0;
+  }
+
+  .blocklyHorizontalTreeRtl {
+    float: right;
+    margin: 1px 0 8px 5px;
+  }
+
+  .blocklyToolboxDiv[dir="RTL"] .blocklyTreeRow {
+    margin-left: 8px;
+  }
+
+  .blocklyTreeRow:hover {
+    color: var(--colour-toolboxHover);
+  }
+
+  .blocklyTreeSeparator {
+    display: none;
+  }
+
+  .blocklyTreeSeparatorHorizontal {
+    border-right: solid #e5e5e5 1px;
+    width: 0;
+    padding: 5px 0;
+    margin: 0 5px;
+  }
+
+  .blocklyTreeIcon {
+    background-image: url(<<<PATH>>>/sprites.png);
+    height: 16px;
+    vertical-align: middle;
+    width: 16px;
+  }
+
+  .blocklyTreeIconClosedLtr {
+    background-position: -32px -1px;
+  }
+
+  .blocklyTreeIconClosedRtl {
+    background-position: 0px -1px;
+  }
+
+  .blocklyTreeIconOpen {
+    background-position: -16px -1px;
+  }
+
+  .blocklyTreeSelected>.blocklyTreeIconClosedLtr {
+    background-position: -32px -17px;
+  }
+
+  .blocklyTreeSelected>.blocklyTreeIconClosedRtl {
+    background-position: 0px -17px;
+  }
+
+  .blocklyTreeSelected>.blocklyTreeIconOpen {
+    background-position: -16px -17px;
+  }
+
+  .blocklyTreeIconNone,
+  .blocklyTreeSelected>.blocklyTreeIconNone {
+    background-position: -48px -1px;
+  }
+
+  .blocklyTreeLabel {
+    cursor: default;
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: .65rem;
+    padding: 0 3px;
+    vertical-align: middle;
+    width: 60px;
+    text-align: center;
+  }
+
+  .blocklyTreeSelected .blocklyTreeLabel {
+    color: inherit;
+  }
+
+  .blocklyToolboxDelete .blocklyTreeLabel {
+    cursor: url("<<<PATH>>>/handdelete.cur"), auto;
+  }
+
+  .blocklyTreeSelected {
+    background-color: var(--colour-toolboxSelected);
+  }
+
+  .blocklyDropDownDiv .goog-slider-horizontal {
+    margin: 8px;
+    height: 22px;
+    width: 150px;
+    position: relative;
+    outline: none;
+    border-radius: 11px;
+    margin-bottom: 20px;
+  }
+
+  .blocklyDropDownDiv .goog-slider-horizontal .goog-slider-thumb {
+    width: 26px;
+    height: 26px;
+    top: -1px;
+    position: absolute;
+    background-color: white;
+    border-radius: 100%;
+    -webkit-box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);
+    -moz-box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);
+    box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.15);
+  }
+
+  .scratchEyedropper {
+    background: none;
+    outline: none;
+    border: none;
+    width: 100%;
+    text-align: center;
+    border-top: 1px solid #ddd;
+    padding-top: 5px;
+    cursor: pointer;
+  }
+
+  .scratchColourPickerLabel {
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 0.65rem;
+    color: var(--colour-toolboxText);
+    margin: 8px;
+  }
+
+  .scratchColourPickerLabelText {
+    font-weight: bold;
+  }
+
+  .scratchColourPickerReadout {
+    margin-left: 10px;
+  }
+
+  .scratchMatrixButtonDiv {
+    width: 50%;
+    text-align: center;
+    float: left;
+  }
+
+  .scratchNotePickerKeyLabel {
+    font-family: "Helvetica Neue", Helvetica, sans-serif;
+    font-size: 0.75rem;
+    fill: var(--colour-textFieldText);
+    pointer-events: none;
+  }
 
   /* Copied from: goog/css/menu.css */
   /*
@@ -1033,28 +930,28 @@ Blockly.Css.CONTENT = [
    * @author attila@google.com (Attila Bodis)
    */
 
-  '.blocklyWidgetDiv .goog-menu {',
-    'background: #fff;',
-    'border-color: #ccc #666 #666 #ccc;',
-    'border-style: solid;',
-    'border-width: 1px;',
-    'cursor: default;',
-    'font: normal 13px "Helvetica Neue", Helvetica, sans-serif;',
-    'margin: 0;',
-    'outline: none;',
-    'padding: 4px 0;',
-    'position: absolute;',
-    'overflow-y: auto;',
-    'overflow-x: hidden;',
-    'z-index: 20000;',  /* Arbitrary, but some apps depend on it... */
-  '}',
-
-  '.blocklyDropDownDiv .goog-menu {',
-    'cursor: default;',
-    'font: normal 13px "Helvetica Neue", Helvetica, sans-serif;',
-    'outline: none;',
-    'z-index: 20000;',  /* Arbitrary, but some apps depend on it... */
-  '}',
+  .blocklyWidgetDiv .goog-menu {
+    background: #fff;
+    border-color: #ccc #666 #666 #ccc;
+    border-style: solid;
+    border-width: 1px;
+    cursor: default;
+    font: normal 13px "Helvetica Neue", Helvetica, sans-serif;
+    margin: 0;
+    outline: none;
+    padding: 4px 0;
+    position: absolute;
+    overflow-y: auto;
+    overflow-x: hidden;
+    z-index: 20000;  /* Arbitrary, but some apps depend on it... */
+  }
+
+  .blocklyDropDownDiv .goog-menu {
+    cursor: default;
+    font: normal 13px "Helvetica Neue", Helvetica, sans-serif;
+    outline: none;
+    z-index: 20000;  /* Arbitrary, but some apps depend on it... */
+  }
 
   /* Copied from: goog/css/menuitem.css */
   /*
@@ -1085,165 +982,165 @@ Blockly.Css.CONTENT = [
    * on the BiDi flipping by the CSS compiler.  That's why we're not adding the
    * #noflip to .goog-menuitem.
    */
-  '.blocklyWidgetDiv .goog-menuitem {',
-    'color: #000;',
-    'font: normal 13px "Helvetica Neue", Helvetica, sans-serif;',
-    'list-style: none;',
-    'margin: 0;',
+  .blocklyWidgetDiv .goog-menuitem {
+    color: #000;
+    font: normal 13px "Helvetica Neue", Helvetica, sans-serif;
+    list-style: none;
+    margin: 0;
      /* 28px on the left for icon or checkbox; 7em on the right for shortcut. */
-    'padding: 4px 7em 4px 28px;',
-    'white-space: nowrap;',
-  '}',
-
-  '.blocklyDropDownDiv .goog-menuitem {',
-    'color: $colour_text;',
-    'font: normal 13px "Helvetica Neue", Helvetica, sans-serif;',
-    'font-weight: bold;',
-    'list-style: none;',
-    'margin: 0;',
-    'min-height: 24px;',
+    padding: 4px 7em 4px 28px;
+    white-space: nowrap;
+  }
+
+  .blocklyDropDownDiv .goog-menuitem {
+    color: var(--colour-text);
+    font: normal 13px "Helvetica Neue", Helvetica, sans-serif;
+    font-weight: bold;
+    list-style: none;
+    margin: 0;
+    min-height: 24px;
      /* 28px on the left for icon or checkbox; 7em on the right for shortcut. */
-    'padding: 4px 7em 4px 28px;',
-    'white-space: nowrap;',
-  '}',
+    padding: 4px 7em 4px 28px;
+    white-space: nowrap;
+  }
 
   /* BiDi override for the resting state. */
   /* #noflip */
-  '.blocklyWidgetDiv .goog-menuitem.goog-menuitem-rtl, ',
-  '.blocklyDropDownDiv .goog-menuitem.goog-menuitem-rtl {',
+  .blocklyWidgetDiv .goog-menuitem.goog-menuitem-rtl, ,
+  .blocklyDropDownDiv .goog-menuitem.goog-menuitem-rtl {
      /* Flip left/right padding for BiDi. */
-    'padding-left: 7em;',
-    'padding-right: 28px;',
-  '}',
+    padding-left: 7em;
+    padding-right: 28px;
+  }
 
   /* If a menu doesn't have checkable items or items with icons, remove padding. */
-  '.blocklyWidgetDiv .goog-menu-nocheckbox .goog-menuitem,',
-  '.blocklyWidgetDiv .goog-menu-noicon .goog-menuitem, ',
-  '.blocklyDropDownDiv .goog-menu-nocheckbox .goog-menuitem,',
-  '.blocklyDropDownDiv .goog-menu-noicon .goog-menuitem { ',
-    'padding-left: 12px;',
-  '}',
+  .blocklyWidgetDiv .goog-menu-nocheckbox .goog-menuitem,
+  .blocklyWidgetDiv .goog-menu-noicon .goog-menuitem, ,
+  .blocklyDropDownDiv .goog-menu-nocheckbox .goog-menuitem,
+  .blocklyDropDownDiv .goog-menu-noicon .goog-menuitem { ,
+    padding-left: 12px;
+  }
 
   /*
    * If a menu doesn't have items with shortcuts, leave just enough room for
    * submenu arrows, if they are rendered.
    */
-  '.blocklyWidgetDiv .goog-menu-noaccel .goog-menuitem, ',
-  '.blocklyDropDownDiv .goog-menu-noaccel .goog-menuitem {',
-    'padding-right: 20px;',
-  '}',
+  .blocklyWidgetDiv .goog-menu-noaccel .goog-menuitem, ,
+  .blocklyDropDownDiv .goog-menu-noaccel .goog-menuitem {
+    padding-right: 20px;
+  }
 
-  '.blocklyWidgetDiv .goog-menuitem-content ',
-  '.blocklyDropDownDiv .goog-menuitem-content {',
-    'color: #000;',
-    'font: normal 13px "Helvetica Neue", Helvetica, sans-serif;',
-  '}',
+  .blocklyWidgetDiv .goog-menuitem-content ,
+  .blocklyDropDownDiv .goog-menuitem-content {
+    color: #000;
+    font: normal 13px "Helvetica Neue", Helvetica, sans-serif;
+  }
 
   /* State: disabled. */
-  '.blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-accel,',
-  '.blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-content, ',
-  '.blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-accel,',
-  '.blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-content {',
-    'color: #ccc !important;',
-  '}',
-
-  '.blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-icon, ',
-  '.blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-icon {',
-    'opacity: 0.3;',
-    '-moz-opacity: 0.3;',
-    'filter: alpha(opacity=30);',
-  '}',
+  .blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-accel,
+  .blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-content, ,
+  .blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-accel,
+  .blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-content {
+    color: #ccc !important;
+  }
+
+  .blocklyWidgetDiv .goog-menuitem-disabled .goog-menuitem-icon, ,
+  .blocklyDropDownDiv .goog-menuitem-disabled .goog-menuitem-icon {
+    opacity: 0.3;
+    -moz-opacity: 0.3;
+    filter: alpha(opacity=30);
+  }
 
   /* State: hover. */
-  '.blocklyWidgetDiv .goog-menuitem-highlight,',
-  '.blocklyWidgetDiv .goog-menuitem-hover {',
-    'background-color: #d6e9f8;',
-     /* Use an explicit top and bottom border so that the selection is visible',
+  .blocklyWidgetDiv .goog-menuitem-highlight,
+  .blocklyWidgetDiv .goog-menuitem-hover {
+    background-color: #d6e9f8;
+     /* Use an explicit top and bottom border so that the selection is visible
       * in high contrast mode. */
-    'border-color: #d6e9f8;',
-    'border-style: dotted;',
-    'border-width: 1px 0;',
-    'padding-bottom: 3px;',
-    'padding-top: 3px;',
-  '}',
-
-  '.blocklyDropDownDiv .goog-menuitem-highlight,',
-  '.blocklyDropDownDiv .goog-menuitem-hover {',
-    'background-color: $colour_menuHover;',
-  '}',
+    border-color: #d6e9f8;
+    border-style: dotted;
+    border-width: 1px 0;
+    padding-bottom: 3px;
+    padding-top: 3px;
+  }
+
+  .blocklyDropDownDiv .goog-menuitem-highlight,
+  .blocklyDropDownDiv .goog-menuitem-hover {
+    background-color: var(--colour-menuHover);
+  }
 
   /* State: selected/checked. */
-  '.blocklyWidgetDiv .goog-menuitem-checkbox,',
-  '.blocklyWidgetDiv .goog-menuitem-icon, ',
-  '.blocklyDropDownDiv .goog-menuitem-checkbox,',
-  '.blocklyDropDownDiv .goog-menuitem-icon {',
-    'background-repeat: no-repeat;',
-    'height: 16px;',
-    'left: 6px;',
-    'position: absolute;',
-    'right: auto;',
-    'vertical-align: middle;',
-    'width: 16px;',
-  '}',
-
-  '.blocklyWidgetDiv .goog-option-selected .goog-menuitem-checkbox,',
-  '.blocklyWidgetDiv .goog-option-selected .goog-menuitem-icon,',
-  '.blocklyDropDownDiv .goog-option-selected .goog-menuitem-checkbox,',
-  '.blocklyDropDownDiv .goog-option-selected .goog-menuitem-icon {',
+  .blocklyWidgetDiv .goog-menuitem-checkbox,
+  .blocklyWidgetDiv .goog-menuitem-icon, ,
+  .blocklyDropDownDiv .goog-menuitem-checkbox,
+  .blocklyDropDownDiv .goog-menuitem-icon {
+    background-repeat: no-repeat;
+    height: 16px;
+    left: 6px;
+    position: absolute;
+    right: auto;
+    vertical-align: middle;
+    width: 16px;
+  }
+
+  .blocklyWidgetDiv .goog-option-selected .goog-menuitem-checkbox,
+  .blocklyWidgetDiv .goog-option-selected .goog-menuitem-icon,
+  .blocklyDropDownDiv .goog-option-selected .goog-menuitem-checkbox,
+  .blocklyDropDownDiv .goog-option-selected .goog-menuitem-icon {
      /* Client apps may override the URL at which they serve the sprite. */
-    'background: url(<<<PATH>>>/sprites.png) no-repeat -48px -16px !important;',
-    'position: static;', /* Scroll with the menu. */
-    'float: left;',
-    'margin-left: -24px;',
-  '}',
+    background: url(<<<PATH>>>/sprites.png) no-repeat -48px -16px !important;
+    position: static; /* Scroll with the menu. */
+    float: left;
+    margin-left: -24px;
+  }
 
   /* BiDi override for the selected/checked state. */
   /* #noflip */
-  '.blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-checkbox,',
-  '.blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-icon,',
-  '.blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-checkbox,',
-  '.blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-icon {',
+  .blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-checkbox,
+  .blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-icon,
+  .blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-checkbox,
+  .blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-icon {
      /* Flip left/right positioning. */
-     'float: right;',
-     'margin-right: -24px;',
-  '}',
+     float: right;
+     margin-right: -24px;
+  }
 
   /* Keyboard shortcut ("accelerator") style. */
-  '.blocklyWidgetDiv .goog-menuitem-accel, ',
-  '.blocklyDropDownDiv .goog-menuitem-accel {',
-    'color: #999;',
+  .blocklyWidgetDiv .goog-menuitem-accel, ,
+  .blocklyDropDownDiv .goog-menuitem-accel {
+    color: #999;
      /* Keyboard shortcuts are untranslated; always left-to-right. */
      /* #noflip */
-    'direction: ltr;',
-    'left: auto;',
-    'padding: 0 6px;',
-    'position: absolute;',
-    'right: 0;',
-    'text-align: right;',
-  '}',
+    direction: ltr;
+    left: auto;
+    padding: 0 6px;
+    position: absolute;
+    right: 0;
+    text-align: right;
+  }
 
   /* BiDi override for shortcut style. */
   /* #noflip */
-  '.blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-accel, ',
-  '.blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-accel {',
+  .blocklyWidgetDiv .goog-menuitem-rtl .goog-menuitem-accel, ,
+  .blocklyDropDownDiv .goog-menuitem-rtl .goog-menuitem-accel {
      /* Flip left/right positioning and text alignment. */
-    'left: 0;',
-    'right: auto;',
-    'text-align: left;',
-  '}',
+    left: 0;
+    right: auto;
+    text-align: left;
+  }
 
   /* Mnemonic styles. */
-  '.blocklyWidgetDiv .goog-menuitem-mnemonic-hint, ',
-  '.blocklyDropDownDiv .goog-menuitem-mnemonic-hint {',
-    'text-decoration: underline;',
-  '}',
-
-  '.blocklyWidgetDiv .goog-menuitem-mnemonic-separator, ',
-  '.blocklyDropDownDiv .goog-menuitem-mnemonic-separator {',
-    'color: #999;',
-    'font-size: 12px;',
-    'padding-left: 4px;',
-  '}',
+  .blocklyWidgetDiv .goog-menuitem-mnemonic-hint, ,
+  .blocklyDropDownDiv .goog-menuitem-mnemonic-hint {
+    text-decoration: underline;
+  }
+
+  .blocklyWidgetDiv .goog-menuitem-mnemonic-separator, ,
+  .blocklyDropDownDiv .goog-menuitem-mnemonic-separator {
+    color: #999;
+    font-size: 12px;
+    padding-left: 4px;
+  }
 
   /* Copied from: goog/css/menuseparator.css */
   /*
@@ -1259,93 +1156,94 @@ Blockly.Css.CONTENT = [
    * @author attila@google.com (Attila Bodis)
    */
 
-  '.blocklyWidgetDiv .goog-menuseparator, ',
-  '.blocklyDropDownDiv .goog-menuseparator {',
-    'border-top: 1px solid #ccc;',
-    'margin: 4px 0;',
-    'padding: 0;',
-  '}',
-
-  '.blocklyFlyoutCheckbox {',
-    'fill: white;',
-    'stroke: #c8c8c8;',
-  '}',
-
-  '.checked > .blocklyFlyoutCheckbox {',
-    'fill: ' + Blockly.Colours.motion.primary + ';',
-    'stroke: ' + Blockly.Colours.motion.tertiary + ';',
-  '}',
-
-  '.blocklyFlyoutCheckboxPath {',
-    'fill: transparent;',
-    'stroke: white;',
-    'stroke-width: 3;',
-    'stroke-linecap: round;',
-    'stroke-linejoin: round;',
-  '}',
-
-  '.scratchCategoryMenu {',
-    'width: 60px;',
-    'background: $colour_toolbox;',
-    'color: $colour_toolboxText;',
-    'font-size: .7rem;',
-    'user-select: none;',
-    '-webkit-user-select: none;',
-    '-moz-user-select: none;',
-    '-ms-user-select: none;',
-  '}',
-
-  '.scratchCategoryMenuHorizontal {',
-    'width: 100%;',
-    'height: 50px;',
-    'background: $colour_toolbox;',
-    'color: $colour_toolboxText;',
-    'font-size: .7em;',
-    'user-select: none;',
-    '-webkit-user-select: none;',
-    '-moz-user-select: none;',
-    '-ms-user-select: none;',
-  '}',
-
-  '.scratchCategoryMenuHorizontal .scratchCategoryMenuRow {',
-    'float: left;',
-    'margin: 3px;',
-  '}',
-
-  '.scratchCategoryMenuRow {',
-  '}',
-
-  '.scratchCategoryMenuItem {',
-    'padding: 0.375rem 0px;',
-    'cursor: pointer;',
-    'text-align: center;',
-  '}',
-
-  '.scratchCategoryMenuHorizontal .scratchCategoryMenuItem {',
-    'padding: 6px 5px;',
-  '}',
-
-  '.scratchCategoryMenuItem.categorySelected {',
-    'background: $colour_toolboxSelected;',
-  '}',
-
-  '.scratchCategoryItemBubble {',
-    'width: 1.25rem;',
-    'height: 1.25rem;',
-    'border: 1px solid;',
-    'border-radius: 100%;',
-    'margin: 0 auto 0.125rem;',
-  '}',
-
-  '.scratchCategoryItemIcon {',
-    'width: 1.25rem;',
-    'height: 1.25rem;',
-    'margin: 0 auto 0.125rem;',
-    'background-size: 100%;',
-  '}',
-
-  '.scratchCategoryMenuItem:hover {',
-    'color: $colour_toolboxHover !important;',
-  '}',
-  ''
-];
+  .blocklyWidgetDiv .goog-menuseparator, ,
+  .blocklyDropDownDiv .goog-menuseparator {
+    border-top: 1px solid #ccc;
+    margin: 4px 0;
+    padding: 0;
+  }
+
+  .blocklyFlyoutCheckbox {
+    fill: white;
+    stroke: #c8c8c8;
+  }
+
+  .checked > .blocklyFlyoutCheckbox {
+    fill: var(--colour-motion-primary);
+    stroke: var(--colour-motion-tertiary);
+  }
+
+  .blocklyFlyoutCheckboxPath {
+    fill: transparent;
+    stroke: white;
+    stroke-width: 3;
+    stroke-linecap: round;
+    stroke-linejoin: round;
+  }
+
+  .scratchCategoryMenu {
+    width: 60px;
+    background: var(--colour-toolbox);
+    color: var(--colour-toolboxText);
+    font-size: .7rem;
+    user-select: none;
+    -webkit-user-select: none;
+    -moz-user-select: none;
+    -ms-user-select: none;
+  }
+
+  .scratchCategoryMenuHorizontal {
+    width: 100%;
+    height: 50px;
+    background: var(--colour-toolbox);
+    color: var(--colour-toolboxText);
+    font-size: .7em;
+    user-select: none;
+    -webkit-user-select: none;
+    -moz-user-select: none;
+    -ms-user-select: none;
+  }
+
+  .scratchCategoryMenuHorizontal .scratchCategoryMenuRow {
+    float: left;
+    margin: 3px;
+  }
+
+  .scratchCategoryMenuRow {
+  }
+
+  .scratchCategoryMenuItem {
+    padding: 0.375rem 0px;
+    cursor: pointer;
+    text-align: center;
+  }
+
+  .scratchCategoryMenuHorizontal .scratchCategoryMenuItem {
+    padding: 6px 5px;
+  }
+
+  .scratchCategoryMenuItem.categorySelected {
+    background: var(--colour-toolboxSelected);
+  }
+
+  .scratchCategoryItemBubble {
+    width: 1.25rem;
+    height: 1.25rem;
+    border: 1px solid;
+    border-radius: 100%;
+    margin: 0 auto 0.125rem;
+  }
+
+  .scratchCategoryItemIcon {
+    width: 1.25rem;
+    height: 1.25rem;
+    margin: 0 auto 0.125rem;
+    background-size: 100%;
+  }
+
+  .scratchCategoryMenuItem:hover {
+    color: $colour_toolboxHover !important;
+  }
+`;
+
+Blockly.Css.register(styles);
diff --git a/src/index.js b/src/index.js
index bd0320177a..b51d0a97e2 100644
--- a/src/index.js
+++ b/src/index.js
@@ -16,6 +16,7 @@ import '../blocks_vertical/operators.js';
 import '../blocks_vertical/sensing.js';
 import '../blocks_vertical/sound.js';
 import * as scratchBlocksUtils from '../core/scratch_blocks_utils.js';
+import '../core/css.js';
 import {
   ContinuousToolbox,
   ContinuousFlyout,
@@ -38,4 +39,6 @@ export function inject(container, options) {
   });
   const workspace = Blockly.inject(container, options);
   return workspace;
-}
\ No newline at end of file
+}
+
+Blockly.Scrollbar.scrollbarThickness = Blockly.Touch.TOUCH_ENABLED ? 14 : 11;