Board Thread:Support Requests - Designing Your Wiki/@comment-6900511-20130305212323/@comment-4018164-20130306094324

Like 65.92.180.137 said, an admin can add a background via the Theme Designer, but note that there is a limitation on the file size which must me under 150KB. It can be achived using a JPG file with a small compression for loosing a large file size yet not loosing important details.

Also, you can apply backgrounds using your MediaWiki:Wikia.css by adding: And replace YOURIMAGE with your image URL. You can also apply it on a certain namespace. For instance, for applying it to project pages, add: Though if you want to apply it wiki-wide, the Theme Designer is the best.