Manual:$wgAllowSiteCSSOnRestrictedPages

ResourceLoader: $wgAllowSiteCSSOnRestrictedPages
Allow site-wide Cascading Style Sheets (CSS) on restricted special pages
Introduced in version:1.23.7 (Gerrit change 165979; git #I1bf4dd1)
Removed in version:still in use
Allowed values:(boolean)
Default value:false

Details edit

Many wikis use pages like MediaWiki:Common.css to create a custom 'theme' for their wiki. However, due to security concerns discussed in task T72672, site-wide CSS on restricted special pages was disabled. By default such style sheets no longer load on login or preference pages creating an inconsistent user interface. This configuration parameter allows to re-enable site-wide CSS on restricted special pages.

If using MobileFrontend extension note that $wgMFSiteStylesRenderBlocking also needs to be enabled for this to work.

See also edit