The stuff inside the curly braces—the properties and values—that’s where the cosmetic problems get solved. It’s also the stuff that you can look up; I certainly don’t try to store all possible CSS properties and values in my head. It’s also easy to evaluate: Does it make the thing look like you want it to look? Yes? Good. It works.
The stuff outside the curly braces—the selectors—that’s harder to judge. It needs to be evaluated with lots of “what ifs”: What if this selects something you didn’t intend to? What if the markup changes? What if someone else writes some CSS that negates this?