what do you mean by that effect? the value of your z-index will just determine the value of your box in your layout..
example:
[quote]<div style="position: absolute; overflow: auto; width: 255px; height: 270px; [b]z-index: 3[/b]; left: 296px; top: 316px" id="ayer3">[/quote]
[b]EDITED:[/b]
z-index will determine which box will overlap