This question has nothing to do with font sizing in the css, what I would like to know is how do you work out the em or percentage for padding/padding-left/top/bottom and margin/margin-left/top/bottom as I was having a look at the bostonglobe.com css and when can you use em or percentage in the css.
Example of css in the bostonglobe:
.weather p {
	margin-left: 1%;
	text-align: center;
	width: 25%;			/* 60 / 240 */
thanks for explanation