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. Ev...