Bootstrap系列 -- 40. 导航条二级菜单

​​https://blog.51cto.com/u_14071312​​

　　在导航条中添加二级菜单也非常简单

<div class="navbar navbar-default" role="navigation">
  　<div class="navbar-header">
  　    <a href="##" class="navbar-brand">导航条a>
  　div>
    <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="##">CSS3a>li>
            <li><a href="##">JavaScripta>li>
            <li class="disabled"><a href="##">PHPa>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>div>