这样对的吧
<style type="text/css">
/*在此定义相关样式，控制列表的显示形式*/
li{
width:50px;
height:30px;
text-align:center;
float:left;
list-style-type: none;
}
ul li div{
display:block;
}
a,a:visited{
color:black;
text-decoration: none
}
a:hover,a:active{
color:white;
background:#BE3948;
}
</style>
</head>
<body>
<h3>课程难度</h3>
<ul>
<li> <div><a class="link" href="#">全部</a></div> </li>
<li><div><a class="link" href="#">初级</a></div></li>
<li><div><a class="link" href="#">中级</a></div></li>
<li><div><a class="link" href="#">高级</a></div></li>
</ul>
