For as long as I've been writing CSS, there's been one direction it refused to look: up. You could style a child based on its parent all day long, but the second you wanted a parent to react to something happening inside it — a checked checkbox, an invalid field, a filled-in input — you were reaching for JavaScript. Every time. It didn't matter how small the interaction was.
:has() breaks that rule on purpose, and it's been safe to use in production for a while now — it's supported across Chrome, Edge, Firefox, Safari, and Opera, no polyfill required. I didn't fully appreciate what that meant until I rebuilt a form I'd been maintaining for two years and deleted most of the JavaScript in it. Not all of it — I'll get to where it still earns its place — but most.
The rule CSS used to have
/* This has always worked: style a child based on the parent */
.card.featured .title { color: gold; }
