Line 146 of ./resources/lib/ooui/oojs-ui-core-wikimediaui.css
- https://phabricator.wikimedia.org/source/mediawiki/browse/master/resources/lib/ooui/oojs-ui-core-wikimediaui.css$146
- https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/refs/heads/master/resources/lib/ooui/oojs-ui-core-wikimediaui.css#146
- https://github.com/wikimedia/mediawiki/blob/master/resources/lib/ooui/oojs-ui-core-wikimediaui.css#L146
background-color: rgba(0, 24, 73, 7/255);
This is not CSS. It looks like LESS, and it is being delivered client-side for web browsers to process, and it doesn't render correctly. This is not the only CSS/LESS issue, but is one of the first I stumbled upon yesterday while working on trying to fix something else.