Transparencecssmenu如何制作透明的CSS菜单

body{
font: 80% Arial,sans-serif;
background: #666;
}
#nav{
width: 170px;
background: url(navbg.gif) bottom;
list-style-type: none;
margin: 0;
padding: 0;
}
#nav a{
display: block;
width: 170px;
line-height: 25px;
text-decoration: none;
color: #333;
text-indent: 10px;
font-weight: bold;
background: url(nav2.png);
}
#nav a:hover{
background: none;
color: #999;
}

<!--[if gte IE 5.5]>
<style type=\"text/css\">
#nav a{background: none;
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale', src='nav2.png')}
#nav a:hover{filter: none}
</style>
<![endif]-->