Say you have the following css applied to a div tag .divtagABS { position: absolute; margin-left: auto; margin-right:auto; } the margin-left and margin-right does not take effect but if you have relative, it works fine i.e. ,divtagREL { position: relative; margin-left: auto; margin-right:auto; } why is that? i just want to center an element can someone explain why setting margins to auto in absolute position does not work?