CSS editor marks some lines as errors even though they're perfectly fine

[zikamatej]

I keep getting error messages in the WP CSS Editor in Live view for pieces of code which are perfectly fine, even according to a CSS3 validator. E.g.:

.post-content a:not(.tags a){
	text-decoration: underline;
}

It's kinda annoying. Please update it to relevantly mirror CSS versions and standards.

[zikamatej]

Customizer CSS error

[joyously]

very similar to https://core.trac.wordpress.org/ticket/44471 (and its duplicates)

[sabernhardt]

#44471 disabled CSS linting, and now the code editor does not give errors for selectors such as
.post-content a:not(.tags a)