Board Thread:Support Requests - Designing Your Wiki/@comment-3387692-20130225021638/@comment-168424-20130227235731

FYI, you should probably experiment with w:c:batenkaitos:Special:MyPage/wikia.css before you add CSS for just your user page to the site-wide CSS page. It's just safer that way. Once it works on your personal CSS page, you can copy it to the site-wide one (w:c:batenkaitos:MediaWiki:Wikia.css), if necessary.

Oh also, you should probably re-save the image you're planning to use as a higher compression JPEG. Loading a 1.2 MB PNG as a background image is kind of bad for performance.