A lot of these are actually bad practice, or things you should already know. Before you use any of them, you should research each of the rules separately to see

A lot of these are actually bad practice, or things you should already know. Before you use any of them, you should research each of the rules separately to see how they work. Code maintainability is #1 in css, and is the hardest thing to do. The main focus should be on that, and not trying to be clever or tricky.