Help:Extension:GlobalCssJs

The GlobalCssJs extension allow users to create a JavaScript page and a CSS page to be loaded in every wiki of a wiki farm. If you go to Special:Preferences >  on any wiki where the extension is enabled you'll find links to your global scripts and style sheets:  meta:Special:MyPage/global.cssmeta:Special:MyPage/global.js On Wikimedia wikis, these global customizations are hosted on Meta-wiki.

Global style sheets (CSS)
Note: Any  lines must be at the top.

Per-skin customization
Currently the extension does not provide global CSS/JS for specific skins, but it is possible to customize the appearance of a specific skin globally by using classes such as "skin-vector" and "skin-monobook", which are added to the body element automatically by MediaWiki.