PSA: CSS Counters rework

[Daniil Sakhapov]

Hello!

I want to announce that css counters have been reworked and are now up-to-date with the spec.

There are some behaviour changes coming with it, but they will not be noticeable for most use cases. Also, the style containment works correctly now.

Firefox is already up-to-date (with the spec with minor bugs), so we will match them there now.

Cheers,

Daniil