Board Thread:Support Requests - Designing Your Wiki/@comment-44278931-20200810082829/@comment-9605025-20200811154117

It isn't working because you didn't import the CSS. This is a frequent misunderstanding that new/inexperienced users have regarding CSS/JS. MediaWiki does not search your wiki for any and all CSS/JS; it loads a select few predefined titles. So how do you get it to load additional CSS/JS? You have to import them via the titles that are automatically loaded. For information on how to do that, see Help:Including additional CSS and JS.