Board Thread:Support Requests - Designing Your Wikia/@comment-24942359-20140517151016/@comment-856287-20140517162301

You don't need a Global.css. Wikia provides several standardized file names for custom code. "MediaWiki:Common.css" would be the equivalent of a Global.css on Revres'Ym Wiki. However, for most new wikis, you probably want to edit MediaWiki:Wikia.css, which will be applied only to the modern/default Wikia skin (Common.css effects all skins, Oasis and the old Monobook that some users still prefer).

My advice would be to change the design to be close to what you want with the theme designer first, and then customize a few things to match your topic (looks like a Minecraft wiki).

For more info, see Help:Customization policy and Help:JavaScript and CSS Cheatsheet.

Of course, at this early stage you might want to just set up a basic wiki with the theme designer and then focus on building up content to attract visitors. …I have to admit though, I completely redesigned my wiki within a couple days of adopting it 😆. It's hard to resist.