<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>导航代码position:relative</title>
<style type="text/css">

.a1{ width:120px; height:40px; background-color:#F00; position:relative; cursor:pointer; overflow:hidden;}
.a1:hover{ overflow:visible}
.a2{ width:120px; height:40px; background-color:#00F; position:relative; cursor:pointer; top:40px; overflow:hidden;}
.a2:hover{ overflow:visible }
.a3{ width:120px; height:40px; background-color:#0F0; margin-left:120px; cursor:pointer;}
.a4{ width:120px; height:40px; background-color:#FF0; position:relative; cursor:pointer; top:40px; overflow:hidden;}
.a4:hover{ overflow:visible }
.a5{ width:120px; height:40px; background-color:#F90; margin-left:120px; cursor:pointer;}
.a6{ width:120px; height:40px; background-color:#63F; position:relative; cursor:pointer; top:40px; overflow:hidden;}
.a6:hover{ overflow:visible}
.a7{ width:120px; height:40px; background-color:#999; margin-left:120px; cursor:pointer;}
</style>

</head>
<body>

<div class="a1">

<div class="a2"><div class="a3"></div>
</div>

<div class="a4"><div class="a5"></div>
</div>

<div class="a6"><div class="a7"></div>
</div>

</div>

</body>
</html>