GitLab Styles автор baffi

Installation (enable the "has" css attribute)

1. Go to "about:config" in your firefox browser and accept the risk.
2. Search for "layout.css.has-selector.enabled" in the "Search preference name" field
3. double click on "false" on the "layout.css.has-selector.enabled" entry to toggle it to "true"

Finally the css "has" attribute can be used:
https://developer.mozilla.org/en-US/docs/Web/CSS/:has#browser_compatibility