docs: polyfill css :has with postcss plugin

[mattjennings]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

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Polyfills CSS :has using the css-has-pseudo postcss plugin. It also involves a JS polyfill (~12kb). Theoretically solves #2981 ... but I haven't tested this on an affected browser.

There's potential for it to not be perfect (see "Known Shortcomings" section in its readme), but initially it seems OK, but given the CSS+JS size increase + potential issues with docusaurus pages, we'll have to consider if it's worth it or not.

Highlighted section is the polyfill I believe

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[eonarheim]

@mattjennings Awesome I had no idea this was a thing!

[eonarheim]

Bummer looks like safari 13 doesn't like it still in browserstack, I'll try it locally with browserstack to be sure

[mattjennings]

Ahh shoot. I was surprised such a thing existed as well, as I remember this being one of those things that you couldn't polyfill for the longest time.

Well, IMO this is a docusaurus issue, and this was probably the best shot we had at doing anything about it save for migrating to an entirely different docs framework. So we may have to close #2981 as a can't/won't fix, unfortunately.

[eonarheim]

Ahh shoot. I was surprised such a thing existed as well, as I remember this being one of those things that you couldn't polyfill for the longest time.

Well, IMO this is a docusaurus issue, and this was probably the best shot we had at doing anything about it save for migrating to an entirely different docs framework. So we may have to close #2981 as a can't/won't fix, unfortunately.

Agreed, I'll open a bug against docusaurus and close ours

[eonarheim]

Closing for now, opened an issue on docusaurus facebook/docusaurus#10074