[kerkeslager]

> You'd have to watch with a MutationObserver and then propagate the change to every instance of a custom element on the page.

This solution works in that you can create a mixin that does this and use it in your custom elements. But if you profile it I think you'll discover it's painfully slow. It's not noticeable if you're using a few custom elements here and there, but if you're, for example, making a table of custom elements, the page will load slowly.

[webstrand]

Yeah, that's exactly my experience. I built a framework for quickly prototyping with web components before I discovered the CSS-isolation defect. Sadly it's pretty much killed that idea as unworkable.

<https://codepen.io/webstrand/pen/jOzYVpL> is as far as I got. The FOUS is pretty annoying, too, before the templates get properly registered. But I could live with that.