Board Thread:Support Requests - Getting Technical/@comment-876677-20151218105403/@comment-26843745-20151218114736

I highly doubt it is possible, really. People other than you can not see it because personal CSS is supposed to work for its owner only. If you want all users to be able to view certain CSS changes, then you should use MediaWiki:Wikia.css, that is if you are an administrator on that wiki.