You paste a snippet from a tutorial. Half your app's buttons change color. The snippet had .btn in it, and so does your codebase. Nothing logged the collision — CSS resolves duplicates silently, by source order, and whichever selector loaded last just won.
Every dev who's copy-pasted CSS has hit some version of this. It's the most common way styles regress in a codebase and the least often called out.
I ship 2,768 CSS demos across 138 collections on codefronts.com, all hand-written. Every demo has to survive two environments:
My own gallery page — where up to 50 demos render side-by-side under a single stylesheet. If two demos both style .card, one wins and the other breaks in production.
Your project — where the snippet lands next to whatever reset, utility framework, and component library you already have wired up. If my .card beats your .card, I've silently regressed your app.
