According to the spec, one ID should be infinitely more specific than a class. But as it turns out, if you add 256 classes to a single element (same or different) it will override the ID. Dumb little edge case that probably will never be fixed, but interesting. Ryan Seddon digs in a little more.
DigitalOcean joining forces with CSS-Tricks! Special welcome offer: get $100 of free credit.