[ss3000]

> Web components do this with the `:host` selector that styles the component from within its shadow root. The styles applied with the `:host` selector can be overridden by the outside styles, without the component needing to weaken encapsulation by allowing styling from the outside via JS properties.

I don't see how the React approach of accepting styles as JS props is any weaker in terms of encapsulation compared to your example above. If anything, it offers the opportunity for stronger encapsulation because it supports limiting/transforming the styling props we accept through those JS props, and even allows us to define a styling API for our component that's completely independent of CSS semantics, enabling components APIs that can span multiple platforms with independent implementations.

[spankalee]

You're right. If we're talking about only the root element, it is similar to :host, because the custom element is itself stylable from the outside.

What makes me say that encapsulation is weakened is that threading JS property bags to other internal elements is also relatively common, and inline styles don't really offer any encapsulation there. Other selectors in the page can still select and style properties that are not directly styled by the element. I should have clarified that.

Shadow DOM provides true runtime style encapsulation, and the selectors on the page can't select the internal elements at all.

[ss3000]

Ah I see, that makes sense. Shadow DOM definitely offers much stronger style encapsulation than a React component where you can only "enforce" that components shouldn't reach into it to style internals by convention.