CSS1 assumes a simple box-oriented formatting model where each formatted element results in one or more rectangular boxes.
All boxes have a core content area with optional surrounding padding, border and margin areas.
The color and style for the border is set with the border properties. The margins are always transparent, so the parent element will shine through. The following example shows how margins and padding format a 'UL' element with two children. To simplify the diagram there are no borders. But, as the example shows, the placement of an element is relative to ancestors and siblings, so these elements' padding and margin properties have an effect on their children.