Cisco Networking Academy - Fundamentals of Web Design
5.4 Style Sheets and CSS
5.4.11 Padding properties in CSS
In CSS, the padding properties enable you to select how much white space is added between the elements border and content. Negative values are not applicable. All the sides of the padding dimensions including top, right, left, and bottom can be selected and controlled using separate properties. Like with margins and borders, you may also control multiple sides simultaneously.
Padding - Sets the size of the padding between the inside of an element's border (if any) and the element itself. The padding for each side may be set individually using padding-top, padding-right, padding-bottom, and padding-left.