<nav class="navbar navbar-default" role="navigation">
<div class="navbar-header">asdasd
<a href="#" class="navbar-brand">asdasd</a>
</div>
<ul class="nav navbar-nav ">
<li class="active"><a href="#">主页</a></li>
<li><a href="#">微博</a></li>
<li><a href="#">图书</a></li>
</ul>
<div class="nav navbar-nav">
<button class="btn btn-default navbar-btn">button</button>
<button class="btn bg-primary navbar-text">button</button>
<button class="btn btn-success navbar-link">button</button>
</div>
<form class="navbar-form navbar-left" role="search">
<div class="form-group">
<input type="text" class="form-control" placeholder="Search">
</div>
<button type="submit" class="btn btn-primary">搜索</button>
</form>
</nav>
<!-- 又想自适应子元素的高度 ，又想在没有子元素的时候有默认的高度 -->
<div style="border:1px solid red;min-height: 30px;min-width: 600px;">
<div style="width:200px;height:70px;background:green">
asdasd
</div>
</div>
