Storybook: Implement polished's cssVar to add CSS variable support fully to theming.

[bhough]

Is your feature request related to a problem? Please describe.
Previously theming would break when passed a CSS variable due to polished not supporting pulling variable values (https://github.com/storybookjs/storybook/issues/6135). A workaround was put in place (https://github.com/storybookjs/storybook/pull/6939) to guard against this but didn't add the ability to leverage them.

Describe the solution you'd like
We now provide a helper in polished that fetches CSS Variable values (https://polished.js.org/docs/#cssvar) and we'd like to help implement it into theming to provide support for CSS variables.

Describe alternatives you've considered
N/A

Are you able to assist bring the feature to reality?
Yes!

[shilman]

Can you explain the use case a bit more? Sounds like a great improvement but I don't quite get it yet. @ndelangen should be able to help if you have any q's about contributing!

[ndelangen]

@bhough that's great news! We'd love to take a PR fixing this.

What do you think about using that util function in the @storybook/theming's convert util?

[bhough]

@ndelangen Great, convert seems like a logical starting point based on a brief look at the code. I'll put some time in this weekend and see what I can come up with.

[giorgiogalassi]

Hi,

Is this issue fixed?
If yes, how i'm supposed to integrate?

I have a library of ui-components, all written in Stencil.JS, using css-variables.

Regards.

[stale[bot]]

Hi everyone! Seems like there hasn't been much going on in this issue lately. If there are still questions, comments, or bugs, please feel free to continue the discussion. Unfortunately, we don't have time to get to every issue. We are always open to contributions so please send us a pull request if you would like to help. Inactive issues will be closed after 30 days. Thanks!

[stale[bot]]

Hey there, it's me again! I am going close this issue to help our maintainers focus on the current development roadmap instead. If the issue mentioned is still a concern, please open a new ticket and mention this old one. Cheers and thanks for using Storybook!