Remove invalid buttons block CSS property

[mukeshpanchal27]

This will fix for #32434

[talldan]

Thanks for working on this @mukeshpanchal27.

Would you be able to give the PR a proper title like "Fix invalid CSS". The PR titles appear in the changelog, so it's great if there's a readable description.

[talldan]

This is an interesting one, because this is valid CSS and supported by browsers, but the spec this is part of is technically a working draft, which is why the validator has flagged it.

The 'note' part here mentions it:
https://drafts.csswg.org/selectors/#negation

[peterwilsoncc]

The way :not() contributes to specificity is a little strange: the specificity is consistently the value of the most specific selector in the list.

For the existing code, this results in the :not() selector contributing one class to the specificity. Bringing the specificity of the generated selector to 0, 0, 4, 0.

In the proposed code, each instance of the :not() selector contributes one class. Bringing the specificity of the generated selector to 0, 0, 7, 0.

Given the code works in all browsers WP and Gutenberg supports, I'd suggest keeping the code as currently published. The reported validator issue isn't a practical issue.

[desrosj]

I think I agree with leaving this one as is.

@mukeshpanchal27 Do you agree, and are you able to update this PR to address this?

[desrosj]

@mukeshpanchal27 Checking if you're able to add this back to the PR branch.

[mukeshpanchal27]

@desrosj PR updated as requested.