WPT details: https://wpt.fyi/results/css/css-counter-styles/counter-style-access-from-shadow-dom.html https://wpt.fyi/results/css/css-counter-styles/counter-styles-override-in-shadow-dom.html https://wpt.fyi/results/css/css-counter-styles/counter-style-fallbacks-in-shadow-dom.html https://wpt.fyi/results/css/css-counter-styles/counter-styles-shadow-dom-part.html
Allows custom counter styles (@counter-style rules) to be defined with shadow trees, and properly referenced within shadow trees or across shadow boundaries.
Currently, if we want to use a custom counter style in shadow trees, the counter style must be defined in the global namespace (i.e., in the light DOM), which breaks encapsulation. This can be fixed if we allow shadow trees to define their own custom counter styles and handle name scoping and conflicts correctly.
Docs: https://bit.ly/2Gm1oMC
Explainers: https://drafts.csswg.org/css-scoping/#example-f1503361 https://drafts.csswg.org/css-scoping/#example-ee72cb37