Board Thread:Support Requests - Getting Technical/@comment-2255188-20140615163532/@comment-856287-20140616043231

You're running into the issue I've described in detail here.

Basically, Wikia made a change for new wikis that drops the contents of Common.css into the top of Wikia.css and thus breaks any @imports in Wikia.css. Wikia says this is a feature, not a bug. That link offers a solution to this feature.