Add new theme tokens bg-blend, bg-highlight, and border-strong (#39786)

app/javascript/mastodon/features/collections/editor/styles.module.scss

@@ -65,7 +65,7 @@
   border-bottom: 1px solid var(--color-border-primary);
 
   &[data-highlighted='true'] {
-    background: var(--color-bg-overlay-highlight);
+    background: var(--color-bg-highlight);
   }
 
   &[aria-disabled='true'] {

app/javascript/mastodon/features/custom_homepage/styles.module.scss

@@ -79,7 +79,7 @@
   :global(.skeleton) {
     height: 40px;
     border-radius: 12px;
-    background: var(--color-bg-overlay-highlight);
+    background: var(--color-bg-highlight);
   }
 }