代码我知道怎么写，给我注释上什么意思就行。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" " http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns=" http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>三级dropdown弹出菜单</title>
<style type="text/css">
.menu {font-family: arial, sans-serif; width:750px; position:relative; margin:0; font-size:11px; margin:50px 0;}
.menu ul li a, .menu ul li a:visited {display:block; text-decoration:none; color:#000;width:104px; height:20px; text-align:center; color:#fff; border:1px solid #fff; background:#710069; line-height:20px; font-size:11px; overflow:hidden;}
.menu ul {padding:0; margin:0;list-style-type: none; }
.menu ul li {float:left; margin-right:1px; position:relative;}
.menu ul li ul {display: none;}
.menu ul li:hover a {color:#fff; background:#36f;}
.menu ul li:hover ul {display:block; position:absolute; top:21px; left:0; width:105px;}
.menu ul li:hover ul li a.hide {background:#6a3; color:#fff;}
.menu ul li:hover ul li:hover a.hide {background:#6fc; color:#000;}
.menu ul li:hover ul li ul {display: none;}
.menu ul li:hover ul li a {display:block; background:#ddd; color:#000;}
.menu ul li:hover ul li a:hover {background:#6fc; color:#000;}
.menu ul li:hover ul li:hover ul {display:block; position:absolute; left:105px; top:0;}
.menu ul li:hover ul li:hover ul.left {left:-105px;}
</style>