Centering a percent-based div

Question

Recently, a client asked that his site be percent-based rather than pixel-based. The percent was to be set to 80%. As you guys know, it is very easy to center the container

Answer 1

#container { width: 80%; margin: 0 auto; position relative; }

And the element parent of "container" must be position relative or absolute

for example:

body{position:relative;}
#container { width: 80%; margin: 0 auto; position relative; }