True, I don’t have benchmarks, but there was a time period where shadow DOM was popularly disabled due to performance hits, but perhaps it was all the performance hit of polyfills and less efficient implementations in browsers. https://github.com/WICG/construct-stylesheets/blob/gh-pages/... is interesting, though Sass still looks unlikely to be added to the browser so we’ll always need some amount of CSS compilation if you want CSS nesting the way you expect it in Sass. Here’s more documentation on constructible stylesheets: https://developers.google.com/web/updates/2019/02/constructa...

I wasn’t aware of this because this stuff is being developed and released so dang quickly! (I do worry that APIs developed in relative haste might be replaced or iterated on in relative haste, especially if they aren’t adopted widely first...)

Perf boost compared to what? It can't be a FCP perf boost relative to server-side rendered plain old CSS and HTML, because shadow DOM requires client-side JavaScript.

Plain old CSS is able to parse and render before the JS required to launch web components has even finished.

I have the same problem with global styles when using Web Components. Using @import in the components to include the shared style files solve the problem.

you can also use :host, which target the custom element specifically (and using :host on custom-element children does not, from what I recall off hand, get broken when nesting) and then target its children.

Also, css variables can be global and still enter into the shadow-dom unobtrusively (This is without using the polyfills, though, I believe this is a limitation in the polyfills currently, which might be why that part of it has been confusing in the past.).