devi modificare lo z-index,
gioca un po' con questo esempio
codice:
<html>
<head>
<title></title>
<style type="text/css">
#lv0 {
top:150px;
left:150px;
background-color:#f0f0f0;
}
#lv1 {
top:125px;
left:175px;
background-color:#ccffff;
}
#lv2 {
top:155px;
left:225px;
background-color:#99ccff;
}
#lv3 {
top:180px;
left:200px;
background-color:#66ccff;
}
.livello {
position:absolute;
width:170px;
height:170px;
border:1px solid #003366;
}
</style>
<script type="text/javascript">
lvTot=4
function ordina(el){
for(var k=0;k<lvTot;k++){
document.getElementById('lv'+k).style.zIndex=(k==el)?15:10+k
}
}
</script>
</head>
<body>
<div id="lv0" class="livello" style="z-index:10" onmouseover="ordina(0)">lv0</div>
<div id="lv1" class="livello" style="z-index:11" onmouseover="ordina(1)">lv1</div>
<div id="lv2" class="livello" style="z-index:12" onmouseover="ordina(2)">lv2</div>
<div id="lv3" class="livello" style="z-index:13" onmouseover="ordina(3)">lv3</div>
</body>
</html>