Disable down-up animations

Author: agriyakhetarpal

assets/theme-css/sphinx-design/_dropdown.scss

@@ -216,15 +216,6 @@ details.sd-dropdown {
   }
 }
 
-@keyframes rotate-to-negative-180 {
-  from {
-    transform: rotate(0deg) scale(1.1);
-  }
-  to {
-    transform: rotate(-180deg) scale(1.1);
-  }
-}
-
 @keyframes rotate-to-0-from-90 {
   from {
     transform: rotate(90deg) scale(1.1);
@@ -234,11 +225,24 @@ details.sd-dropdown {
   }
 }
 
-@keyframes rotate-to-0-from-negative-180 {
-  from {
-    transform: rotate(-180deg) scale(1.1);
-  }
-  to {
-    transform: rotate(0deg) scale(1.1);
-  }
-}
+// TODO: These keyframes are disabled for now to maintain
+// parity with Sphinx Design upstream, which does not implement
+// the down-up chevron animation.
+
+// @keyframes rotate-to-negative-180 {
+//   from {
+//     transform: rotate(0deg) scale(1.1);
+//   }
+//   to {
+//     transform: rotate(-180deg) scale(1.1);
+//   }
+// }
+
+// @keyframes rotate-to-0-from-negative-180 {
+//   from {
+//     transform: rotate(-180deg) scale(1.1);
+//   }
+//   to {
+//     transform: rotate(0deg) scale(1.1);
+//   }
+// }