nav_mid_li 不在导航栏上剧中？
我按照老师的为什么我的nav_mid_li 不在导航栏上剧中，我的css及html如下：
.nav {
height: 40px;
}
.nav_left {
width: 10px;
background: url(../img/nav_left.jpg) no-repeat;
}
.nav_mid {
width: 980px;
background: url(../img/nav_bg.jpg) repeat-x;
line-height: 40px;
}
.nav_right {
width: 10px;
background: url(../img/nav_right.jpg) no-repeat;
}
.nav_left,.nav_mid,.nav_right {
height: 40px;
float: left;
display: inline;
}
.nav_mid_left,.nav_mid_right{
float: left;
}
.nav_mid_left{
width: 680px;
}
.nav_mid_right{
width: 300px;
}
.nav_mid_left li {
float: left;
list-style-type: none;
width: 100px;
font-family: "微软雅黑";
text-align: center;
}HTML如下：
<div class="nav">
<div class="nav_left"></div>
<div class="nav_mid">
<div class="nav_mid_left">
<ul>
<li><a href="#">首页</a></li>
<li><a href="list.html">关于慕课</a></li>
<li><a href="list.html">新闻动态</a></li>
<li><a href="list.html">课程中心</a></li>
<li><a href="list.html">在线课程</a></li>
<li><a href="list.html">人才招聘</a></li>
</ul>
</div>
<div class="nav_mid_right">
<form action="" method="post">
<input type="text" />
</form>
</div>
</div>
<!--nav_mid结束
作者：350634964@qq.com
时间：2018-06-29
描述：
-->
<div class="nav_right"></div>
</div>
请问有什么错误，求大神。
