求助。前面的都可以，就是最后一步显示不出来display:block
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<style>
*{
padding: 0;
margin: 0;
border: 0;
}
ul{
list-style: none;
}
nav{
background-color: #eee;
width: 600px;
height: 40px;
margin: 0 auto;
}
ul li{
float: left;
position: relative;
line-height: 40px;
text-align: center;
}
a{
text-decoration: none;
display: block;
padding: 0 10px;
}
a:hover{
color: #fff;
background-color: red;
}
#erji li{
float: none;
background-color: #eee;
margin-top: 2px;
}
#erji{
position: absolute;
left: 0px;
top: 40px;
display: none;
}
#erji li a:hover{
background-color: blue;
}
nav ul li:hover ul{
display: block;
}
</style>
<body>
<nav>
<ul>
<li><a href="">首页</a></li>
<li><a href="">课程中心</a>
<ul id="erji">
<li><a href="">javascript</a></li>
<li><a href="">jquery</a></li>
</ul>
</li>
<li><a href="">经典案例</a></li>
<li><a href="">不论是谁</a></li>
<li><a href="">且哦怕</a></li>
</ul>
</nav>
</body>
</html>
