Type, Class and ID Selectors

A selector tells the browser which elements a rule styles (every element of one kind, every element with a class, or the one element with an id), and commas let one rule style several selections at once.

Updated

Cheat sheet: Type, Class and ID Selectors
Category
CSS
Level
Novice
Tags
Class selector, Comment (css), CSS, ID selector, Selector list, Type selector, Universal selector