Red block titles for validation errors

resolves #3599

CHANGELOG-v3.md

@@ -13,6 +13,7 @@
 - Pressing the <kbd>Return</kbd> key (or <kbd>Ctrl</kbd>/<kbd>Command</kbd> + <kbd>Return</kbd>) when a textual cell is focused in an editable table will now change the focus to the same cell in the next row (after creating a new row if necessary.) ([#3576](https://github.com/craftcms/cms/issues/3576))
 - The Password input in the web-based Craft setup wizard now has a “Show” button like other password inputs.
 - The Feed widget now sets the items’ text direction based on the feed’s language.
+- Matrix blocks that contain validation errors now have red titles, to help them stand out when collapsed. ([#3599](https://github.com/craftcms/cms/issues/3599))
 
 ### Fixed
 - Fixed a bug where the “Edit” button on asset editor HUDs didn’t launch the Image Editor if the asset was being edited on another element type’s index page. ([#3575](https://github.com/craftcms/cms/issues/3575))

src/templates/_components/fieldtypes/Matrix/input.html

@@ -15,7 +15,7 @@
                     <input type="hidden" name="{{ name }}[{{ blockId }}][type]" value="{{ block.getType().handle }}">
                     <input type="hidden" name="{{ name }}[{{ blockId }}][enabled]" value="{% if block.enabled %}1{% endif %}">
                     <div class="titlebar">
-                        <div class="blocktype">{{ block.getType().name|t('site') }}</div>
+                        <div class="blocktype{% if block.hasErrors() %} error{% endif %}">{{ block.getType().name|t('site') }}</div>
                         <div class="preview"></div>
                     </div>
                     <div class="checkbox" title="{{ 'Select'|t('app') }}"></div>