Updates to resolve CSS var()

[hughes-ch]

Implements this spec:
https://drafts.csswg.org/css-variables-1/

Includes standard substitution, dependency cycles, and inheritance. I've hooked in the new css/css-variables WPT tests directory and made sure I didn't cause any new failures. Still looks like there's some work to do regarding parsing custom properties and the "var()" function in cssstyle. I've added notes to to-run.yml in places where I was pretty sure the problem was there.

This pull request can be standalone, but it probably works better if it's included with one of these requests from cssstyle:
jsdom/cssstyle#127
jsdom/cssstyle#140

[AshConnolly]

Would love if this got approved! 🙏

[raymondwang]

Any updates here? I've run into this issue as well, and would love to be able to stop using my workaround.

[hughockey]

@raymondwang I'm running into this issue too, I'm curious, what is your workaround?

[raymondwang]

@hughockey I had something else in mind when I first left that comment (pulling the resolved variable value from the element and setting the value of the variable directly onto the element, and using a MutationObserver to keep the value in sync), but ultimately I ended up just spying on document.documentElement.style.setProperty.

[louia]

Any news ?

[effervescentia]

any progress here? I'm planning on adopting vanilla-extract for a new project but it heavily relies on CSS variables for dynamic styling which then renders those aspects of the styling untestable through RTL + jsdom

[nirzafran]

any updates on this? this PR is like 2 years old

[mrpinkcat]

I would be interested in any news on the subject.

[theMasix]

Any update here? It's been 2 years since opening this PR!

[EdgarKisman]

Also waiting for the merge.