User blog comment:DaNASCAT/Technical Update: August 16, 2011/@comment-1091639-20110817131435/@comment-168424-20110818045126

I started customizing my Admin Dashboard via Special:MyPage/wikia.css over at WoWWiki so it would harmonize better with the dark skin. I'm not sure what you mean. Are you asking if it is allowed personally or wiki-wide?

Never mind what I said above. I'm seeing now that Wikia intentionally made it difficult to override the CSS of the Admin Dashboard with Special:MyPage/wikia.css. What a pain.