[selectors] same syntax for custom states and custom selectors

[romainmenke]

• https://github.com/WICG/custom-state-pseudo-class/issues/6
• https://drafts.csswg.org/css-extensions/#custom-selectors

@custom-selector :--heading h1, h2, h3, h4, h5, h6; has been in use for years as a way to declare custom selectors through postcss-custom-selectors

Is it fine that these overlap or does one need to change?

[Loirooriol]

Maybe file an issue in https://github.com/WICG/custom-state-pseudo-class/issues too.

[romainmenke]

Done : https://github.com/WICG/custom-state-pseudo-class/issues/17

[romainmenke]

I think this can be closed after : https://github.com/w3c/csswg-drafts/issues/4805#issuecomment-1663111980 ?