Relative Units:

• em - the 'font-size' of the relevant font

• ex - the 'x-height' of the relevant font

• px - pixels, relative to the viewing device

Absolute Units:

• in - inches

• cm - centimeters

• mm - millimeters

• pt - point - 1/72 of an inch

• pc - pica - 12 points

Examples:

font-size: 1.25em;

border-top-width: 0.5cm;