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line-height: 40px;
text-align: center;
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ul li{
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position: relative;
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ul li ul{
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top:40px;
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ul li ul li{
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background-color: #eee;
margin-top: 2px;
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a:hover{
color: #fff;
background-color: #666;
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ul li ul li{
width: 80px;
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<li class="intro"><a href="#">首页<span>Home</span></a></li>
<li class="intro"><a href="#">课程大厅<span>Course</span></a>
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<li><a href="#">C语言</a></li>
<li><a href="#">Java</a></li>
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<li class="intro"><a href="#">学习中心<span>Learn</span></a>
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<li><a href="#">1</a></li>
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<li><a href="#">3</a></li>
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<li class="intro"><a href="#">经典案例<span>Case</span></a>
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<li><a href="#">5</a></li>
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