In this example box01 and box02 have absolute positioning applied .box01{position:absolute; top:0; left:0;}
.box02{position:absolute; top:0; left:420px;} but the parent box has no positioning specified .mainbox{width:500px; background:#e7e1aa;}

This time the parent box has relative position applied.mainbox{position:relative; width:500px; background:#e7e1aa;} while box01 and box02 are positioned exactly the same as the example above .box01{position:absolute; top:0; left:0;}
.box02{position:absolute; top:0; left:420px;}