lucy24 - 4:36 am on Mar 5, 2012 (gmt 0)
The padding is in addition to the stated width of the element. So's the border, if you've got one.
The picture is at the very top of the page. The innermost box is the size you've set for your element. Everything else-- padding, border, margin-- goes outside. This is nasty and counter-intuitive, but it explains much.
I guess it makes sense if you think of the object as a person. When you put on more clothes, you don't get skinnier to compensate. The clothes make you fatter.