common/static/common/scripts/app.js

@@ -140,6 +140,7 @@
 
           // Show button if item platform matches active platform
           if (itemPlatformBasePrefix.startsWith(activePlatformPrefix)) {
+            item.classList.add('btn-install-action-item-active');
             item.classList.remove('d-none');
           }
         });

common/static/common/styles/_extension.sass

@@ -167,8 +167,9 @@
   .btn-install-action-item
     +margin(3, bottom)
 
-    &:last-child
-      +margin(0, bottom)
+  .btn-install-action-item-active ~ .btn-install-action-item-active
+    border-bottom: thin solid var(--border-color)
+    +padding(3, bottom)
 
   .btn-install-drag,
   .btn-install-drag:active