Quite a few people are replying, asking why CSS nesting can't just work like Sass does.
Well, it can't.
We *all* wish it could.
But it can't because of the way browser parsing engines work: if they see a sequence like `element:pseudo`, they’ll parse the entire style rule as if it were a `property: value` declaration.
So Option 3 vs 4 vs 5 is the our choice for what to do instead.