<div class="navbar navbar-default navbar-fixed-top" role="navigation">
<div class="navbar-header">
　<!-- .navbar-toggle样式用于toggle收缩的内容，即nav-collapse collapse样式所在元素 -->
<button class="navbar-toggle" type="button" data-toggle="collapse" data-target=".navbar-responsive-collapse">
<span class="sr-only">切换导航</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<!-- 确保无论是宽屏还是窄屏，navbar-brand都显示 -->
<a href="##" class="navbar-brand">慕课网</a>
</div>
<!-- 屏幕宽度小于768px时，div.navbar-responsive-collapse容器里的内容都会隐藏，显示icon-bar图标，当点击icon-bar图标时，再展开。屏幕大于768px时，默认显示。 -->
<div class="collapse navbar-collapse navbar-responsive-collapse">
<ul class="nav navbar-nav">
<li class="active"><a href="##">网站首页</a></li>
<li class="dropdown">
<a href="##" data-toggle="dropdown" class="dropdown-toggle">系列教程<span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="##">CSS3</a></li>
<li><a href="##">JavaScript</a></li>
<li class="disabled"><a href="##">PHP</a></li>
</ul>
</li>
<li><a href="##">名师介绍</a></li>
<li><a href="##">成功案例</a></li>
<li><a href="##">关于我们</a></li>
</ul>
<form action="##" class="navbar-form navbar-left" rol="search">
<div class="form-group">
<input type="text" class="form-control" placeholder="请输入关键词" />
</div>
<button type="submit" class="btn btn-default">搜索</button>
</form>
</div>
</div>