dreamweaver里如何做出鼠标悬停出现展开菜单的效果?

<style type="text/css">
<!--
li {
display: block;
padding: 0;
margin: 1px 0 0;
list-style: none;
width:150px;
text-align:center;
background-color:#FFCC33;
}
li a:link,li a:visited{
display:block;
color:#000000;
padding:2px 5px;
height:1%;
}
li a:hover{
font-weight:bold;
position:relative;
background-color:#666666;
}
li ul{
position:absolute;
visibility:hidden;
left:100px;
top:0px;
}
li li {
background-color:#FF6600;
}
li li ul{
position:absolute;
visibility:hidden;
}
li li li {
background-color:#3399FF;
}
li:hover ul{
visibility:visible;
}
li:hover ul ul{
visibility:hidden;
}
li a:hover ul{
visibility:visible;
left:100px;
}
li a:hover ul ul{
visibility:hidden;
}
l