When introducing gadgets it was possible to overwrite CSS rules made in MediaWiki:Common.css or MediaWiki:Monobook.css. Now these ones don't work anymore because of the order in the HTML file. First the Gadget CSSs files are included, then the normal CSS files.
Example: In the german Wikipedia there ist the gadget MediaWiki:Gadget-Personendaten.css, which displays some normally hidden (display: none) metadata (Persondata).
Version: unspecified
Severity: major