Let’s Write Beautiful CSS Comments | Sparkbox
If you don’t comment your CSS, you’ll confuse other people looking at your code, and, more embarrassingly, you’ll confuse future you. If you do comment CSS, everybody will be less confused, and things will be accidentally broken less often. You will be popular and generally well-liked, and people will remember to send you cards on your birthday. Comment more.
Some good advice here on how to write better comments in CSS.