A margin is the space between an element and the elements to its top, left, bottom and right. The margin properties set the size of the top, left, bottom, right and all margins respectively. Possible values Margins can be specified as either a percentage, a length or using the keyword auto.
Margins can be negative values.
A percentage margin value sets the affected margin to that percentage of the width of the parent element . We cover length values in detail in our section on values. Essentially though there are two types of length value. There are absolute values such as px. If you use one of these, the actual length of the margin will always be the same.