As an absolute value As a relative value.
Absolute values have a fixed, specific value.
They let you, the page creator, be exact in your measurements and control the display of your Web pages. When you are using absolute values always remember that the reader might be viewing your page in a different environment from what you expect. Relative values have no fixed, specific value. Rather, they are calculated in comparison to a current value. Indent might be specified in em spaces, which vary with the display size of the text.