This CSS cheat sheet is gonna save me a couple of Google searches next time I start fiddling around with my layout:

Sets the size of the overall margin of an element. Negative values are permitted, but exercise caution. Multiple values start from the top and go clockwise.
H1 {margin: 2em;}
P {0% 5% 0% 5%;}

(from Brett Merkey’s CSS Cheatsheet)