Wikipedia support supplying your own custom.css which is applied whenever you're logged in. See https://www.mediawiki.org/wiki/Help:Extension:GlobalCssJs https

Wikipedia support supplying your own custom.css which is applied whenever you're logged in. See https://www.mediawiki.org/wiki/Help:Extension:GlobalCssJs https://www.mediawiki.org/wiki/Help:Extension:GlobalCssJs