Manual:User group CSS and JavaScript

User group CSS and JavaScript is possible since MediaWiki 1.18 (specifically r82285). This means that CSS and JavaScript can be loaded per user group. CSS and JavaScript pages take the form where X is the user group name.
 * and

The special groups "*" and "user" don't load a specific MediaWiki:Group-X.css or .js page.

Examples:
 * MediaWiki:Group-sysop.css and MediaWiki:Group-sysop.js (code for sysops/administrators)
 * MediaWiki:Group-autoconfirmed.css and MediaWiki:Group-autoconfirmed.js (code for autoconfirmed users)