diff --git a/bolt.css b/bolt.css
index 13a7fe3..e25d912 100644
--- a/bolt.css
+++ b/bolt.css
@@ -500,17 +500,22 @@ progress {
   appearance: none;
   height: 1rem;
   margin: 0.75rem 0;
+  -webkit-appearance: none;
+  -moz-appearance: none;
+  border-radius: var(--border-radius);
+  background-color: var(--background-main);
 }
 
 progress::-webkit-progress-bar {
-  background: var(--background-main);
   box-shadow: 0 2px 3px rgba(0, 0, 0, 0.2) inset;
-  border-radius: var(--highlight-border-radius);
+  border-radius: var(--border-radius);
+  background: none;
 }
-
-progress::-webkit-progress-value {
+progress[value]::-webkit-progress-value {
   background-color: var(--links);
   border-radius: var(--highlight-border-radius);
+  -webkit-transition: inline-size 0.2s ease-in-out;
+  transition: inline-size 0.2s ease-in-out;
 }
 
 progress::-moz-progress-bar {
@@ -518,6 +523,26 @@ progress::-moz-progress-bar {
   border-radius: var(--highlight-border-radius);
 }
 
+progress:indeterminate {
+  background: var(--background-main) linear-gradient(to right, var(--links) 35%, var(--background-main) 35%) top left/150% 150% no-repeat;
+  animation: progress-indeterminate 1s linear infinite;
+}
+progress:indeterminate[value]::-webkit-progress-value {
+  background-color: transparent;
+}
+progress:indeterminate::-moz-progress-bar {
+  background-color: transparent;
+}
+
+@keyframes progress-indeterminate {
+  0% {
+    background-position: 200% 0;
+  }
+  100% {
+    background-position: -200% 0;
+  }
+}
+
 fieldset {
   border: 1px var(--border) solid;
   border-radius: 6px;
diff --git a/index.html b/index.html
index 840233a..39b9c85 100644
--- a/index.html
+++ b/index.html
@@ -402,6 +402,9 @@ <h3 class="demo-header">optgroup</h3>
         <h3 class="demo-header">progress</h3>
         <label for="file">File progress</label>
         <progress id="file" max="100" value="70">70%</progress>
+
+        <label for="indeterminate">Indeterminate progress</label>
+        <progress id="indeterminate"></progress>
       </div>
 
       <!-- output -->