Board Thread:General Discussion/@comment-30064728-20170329235702/@comment-1757994-20170330204318

Wikia strips out inline CSS for mobile users. Wikia also does not load any user-specific or site-specific stylesheets for mobile users. The only stylesheets they load for mobile users are their own.

So unless you can find a Wikia-provided (or MediaWiki-default) style to use on your pages, you cannot style your pages for mobile users.