Board Thread:Support Requests - Designing Your Wiki/@comment-11435437-20131119201125/@comment-4519283-20131120225458

That would be using CSS. It's better to store the CSS on Wikia than use it externally. If you store it externally, the server will have to request the other website, which takes extra time on every page load and can be very hard on your server if you use your wiki a lot. There is also the chance your server will go down, which will cause an error in addition to the CSS not rendering. And if your external server is hacked, depending on what they put on the website, you can be held responsible. So I'm going to explain how to put the CSS directly on Wikia.

There's actually two methods that you can use. The old method is to edit MediaWiki:Wikia.css (or MediaWiki:Monobook.css for Monobook) and put the CSS theme there. Starting December 4 (or earlier if you so request), you can use Special:CSS to edit the CSS on your wiki. Just take the CSS from the external site and put it in the appropriate page listed above. If you need more help, post what's after "supply the following URL" and I can give you more specific instructions.