User blog comment:Kirkburn/Technical Update: October 26, 2015/@comment-5645428-20151027121859/@comment-1251315-20151027123258

You don't really need to use the MediaWiki:Wikia.css page anyway, unless your wiki was made before MediaWiki:Common.css loaded on all skins (it used to be that wiki's made before June 2014 (or somewhere around that) had to have separate css files, but this isn't the case for wiki's after the merge date). Hopefully Wikia will retroactively apply that change to older wiki's as well, since it's somewhat pointless to have to maintain two CSS files :/