分别用html+css,js,jquery实现二级下拉列表

<!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>无标题文档</title>
<style type="text/css">
*{ margin:0px; padding:0px;}
 #menu{ background-color:#eee; width:600px; height:40px; margin:0 auto;}
 ul{ list-style:none;}
 ul li{ float:left;  line-height:40px; text-align:center; position:relative;}
 a{ text-decoration:none; color:#000; display:block; width:90px;}
 a:hover{ color:#FFF; background-color:#666;}
 ul li ul li{ float:none; border-left:none; margin-top:2px; background-color:#eee; } 
 ul li ul{   display:none; width:90px; position:absolute;}
 ul li:hover ul{ display:block;}
  
 
</style>
</head>

<body>
<div id="menu">
   <ul>
   
  <li><a href="#">首页</a></li>
  <li><a href="#">课程大厅</a>
      <ul>
  
   <li><a href="#">JavaScript</a></li>
  <li><a href="#">jQuery</a></li>
  
      </ul>
  
  </li>
  <li><a href="#">学习中心</a>
    <ul>
    <li><a href="#">视频学习</a></li>
      <li><a href="#">案例学习</a></li>
      <li><a href="#">交流平台</a></li>
      </ul>
  </li>
  <li><a href="#">经典案例</a></li>
  <li><a href="#">关于我们</a></li>
  
</ul>


</div> 
          </body>
</html>
<!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>无标题文档</title>
<style type="text/css">
*{ margin:0px; padding:0px;}
body{ font-family:Verdana, Geneva, sans-serif; font-size:14px;}
#nav{ width:600px; height:40px; background-color:#eee; margin:0 auto;}
ul{ list-style:none;}
ul li{ float:left; line-height:40px; text-align:center; width:100px;}

a{ text-decoration:none; color:#000; display:block;}
a:hover{ color:#F00; background-color:#666;}



ul li ul li{ float:none;background-color:#eee; margin:2px 0px;}

ul li ul{ display:none;}



</style>

 <script type="text/javascript">

        function displaySubMenu(li) {

            var subMenu = li.getElementsByTagName("ul")[0];

            subMenu.style.display = "block";

        }

        function hideSubMenu(li) {

            var subMenu = li.getElementsByTagName("ul")[0];

            subMenu.style.display = "none";

        }

    </script>
</head>

<body>
<div id="nav">
<ul>
  <li><a href="#">首页</a></li>
  <li onmouseover="displaySubMenu(this)" onmouseout="hideSubMenu(this)"><a href="#">课程大厅</a>
     <ul>
         <li><a href="#">JavaScript</a></li>
         <li><a href="#">Html/CSS</a></li>
     </ul>  
  </li>
  <li onmouseover="displaySubMenu(this)" onmouseout="hideSubMenu(this)"><a href="#">学习中心</a>
      <ul>
         <li><a href="#">视频学习</a></li>
         <li><a href="#">实例练习</a></li>
         <li><a href="#">问与答</a></li>
     </ul>  
  
  </li>
  <li><a href="#">经典案例</a></li>
  <li><a href="#">关于我们</a></li>
  
</ul>

</div>
</body>
</html>
<!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>无标题文档</title>
<style type="text/css">
*{ margin:0px; padding:0px;}
 #menu{ background-color:#eee; width:600px; height:40px; margin:0 auto;}
 ul{ list-style:none;}
 ul li{ float:left;  line-height:40px; text-align:center; position:relative;}
 a{ text-decoration:none; color:#000; display:block; width:90px;}
 a:hover{ color:#FFF; background-color:#666;}
 ul li ul li{ float:none; border-left:none; margin-top:2px; background-color:#eee; } 
 ul li ul{  width:90px; position:absolute; left:0px; top:40px; display:none;}
 
</style>
<script src="jquery/jquery-1.7.1.min.js"></script>

<script type="text/javascript">
  $(function(){
     $(".navmenu").mouseover(function(){
         $(this).children("ul").show();
         
         
         })
     $(".navmenu").mouseout(function(){
         
         $(this).children("ul").hide();
         
         })
      
      })
  
</script>

</head>

<body>
<div id="menu">
   <ul>
   
  <li><a href="#">首页</a></li>
  <li class="navmenu"><a href="#">课程大厅</a>
      <ul>  
         <li><a href="#">JavaScript</a></li>
         <li><a href="#">jQuery</a></li>
      </ul>
  
  </li>
  <li class="navmenu"><a href="#">学习中心</a>
      <ul>
         <li><a href="#">视频学习</a></li>
         <li><a href="#">案例学习</a></li>
         <li><a href="#">交流平台</a></li>
      </ul>
  </li>
  <li><a href="#">经典案例</a></li>
  <li><a href="#">关于我们</a></li>
  
</ul>


</div> 
          </body>
</html>
原文地址:https://www.cnblogs.com/crazy-zw/p/5476525.html