我的二级栏目为什么没有显示出来呢？
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
*{
margin: 0;
padding: 0;
}
.page{
width: 100%;
height: 1035px;
background: url(img/mo.png.jpg) center top no-repeat;
}
.nav{
width: 160px;
height: auto ;
position: fixed;
left: 0;
top:50%;
margin-top: -103px;
font-family: "微软雅黑";
}
.nav-li{
width:160px ;
height: 40px;
border-bottom: 1px solid #fff;
background: #333;
text-align: center;
line-height: 40px;
color: #fff;
font-size: 16px;
}
.nav-li ul{
width: 160px;
height: auto;
background: #fff;
}
.tit{
width: 160px;
height: 40px;
}
.nav-li ul li{
width: 160px;
height:40px;
border-bottom: 1px dashed #666;
color:#333 ;
text-align: center;
line-height: 40px;
}
</style>
</head>
<body>
<div class="page">
<div class="nav">
<div class="nav-li">
<div class="tit">慕课网的da标题</div>
<ul>
<li >二级栏目</li>
</ul>
</div>
<div class="nav-li" >慕课网的标题</div>
<div class="nav-li">慕课网的标题</div>
<div class="nav-li">慕课网的标题</div>
<div class="nav-li">慕课网的标题</div>
<div class="nav-li">慕课网的标题</div>
</div>
</div>
</body>
</html>
