Bookmarks WebUI: Fix dark mode colors during drag

This CL increases specificity of dark mode CSS for a folder that has
a drag over it to force the CSS to override other colors.

Fixed: 1139798
Change-Id: I6bda5834d06e9d3a4ebd27aea468df3c44a42512
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490680Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819630}

chrome/browser/resources/bookmarks/folder_node.html

@@ -46,9 +46,9 @@
   }
 
   @media (prefers-color-scheme: dark) {
-    .drag-on .menu-label,
-    .drag-on .folder-icon,
-    .drag-on #arrow {
+    #container.drag-on .menu-label,
+    #container.drag-on .folder-icon,
+    #container.drag-on #arrow {
       color: var(--google-grey-refresh-700);
     }
   }