Adobe has produced a tremendously useful resource for anyone working with Shadow DOM and trying to understand where modern CSS features actually stand in practice, not just in theory.

What I especially like here is the framing: not simply “supported” or “unsupported,” but whether a feature is actually advisable in Shadow DOM, how it crosses boundaries, and where browsers still disagree. That’s the kind of nuance you need when you’re building real components instead of admiring specs from afar.