Bootstrap导航菜单实现

<h3>导航栏</h3>
    <nav class="navbar navbar-inverse navbar-fixed-top">
        <div id="navbar" class="navbar-collapse collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="#">Home</a></li>
            <li><a href="#about">About</a></li>
            <li><a href="#contact">Contact</a></li>
            <li class="dropdown">
              <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Dropdown <span class="caret"></span></a>
              <ul class="dropdown-menu" role="menu">
                <li><a href="#">Action</a></li>
                <li><a href="#">Another action</a></li>
                <li class="divider"></li>
                <li class="dropdown-header">Nav header</li>
                <li><a href="#">Separated link</a></li>
              </ul>
            </li>
          </ul>
        </div><!--/.nav-collapse -->
      </div>
    </nav>