Css 如何在悬停而不是单击时制作 Twitter Bootstrap 菜单下拉菜单

body {
  padding-top: 60px;
  padding-bottom: 40px;
}

.sidebar-nav {
  padding: 9px 0;
}

.dropdown-menu .sub-menu {
  left: 100%;
  position: absolute;
  top: 0;
  visibility: hidden;
  margin-top: -1px;
}

.dropdown-menu li:hover .sub-menu {
  visibility: visible;
}

.dropdown:hover .dropdown-menu {
  display: block;
}

.nav-tabs .dropdown-menu,
.nav-pills .dropdown-menu,
.navbar .dropdown-menu {
  margin-top: 0;
}

.navbar .sub-menu:before {
  border-bottom: 7px solid transparent;
  border-left: none;
  border-right: 7px solid rgba(0, 0, 0, 0.2);
  border-top: 7px solid transparent;
  left: -7px;
  top: 10px;
}

.navbar .sub-menu:after {
  border-top: 6px solid transparent;
  border-left: none;
  border-right: 6px solid #fff;
  border-bottom: 6px solid transparent;
  left: 10px;
  top: 11px;
  left: -6px;
}

<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/2.3.2/css/bootstrap.min.css" rel="stylesheet" />

<div class="navbar navbar-fixed-top">
  <div class="navbar-inner">
    <div class="container-fluid">
      <a data-target=".nav-collapse" data-toggle="collapse" class="btn btn-navbar">
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </a>
      <a href="#" class="brand">Project name</a>
      <div class="nav-collapse">
        <ul class="nav">
          <li class="active"><a href="#">Home</a></li>
          <li><a href="#">Link</a></li>
          <li><a href="#">Link</a></li>
          <li><a href="#">Link</a></li>
          <li class="dropdown">
            <a data-toggle="dropdown" class="dropdown-toggle" href="#">Dropdown <b class="caret"></b></a>
            <ul class="dropdown-menu">
              <li>
                <a href="#">2-level Dropdown <i class="icon-arrow-right"></i></a>
                <ul class="dropdown-menu sub-menu">
                  <li><a href="#">Action</a></li>
                  <li><a href="#">Another action</a></li>
                  <li><a href="#">Something else here</a></li>
                  <li class="divider"></li>
                  <li class="nav-header">Nav header</li>
                  <li><a href="#">Separated link</a></li>
                  <li><a href="#">One more separated link</a></li>
                </ul>
              </li>
              <li><a href="#">Another action</a></li>
              <li><a href="#">Something else here</a></li>
              <li class="divider"></li>
              <li class="nav-header">Nav header</li>
              <li><a href="#">Separated link</a></li>
              <li><a href="#">One more separated link</a></li>
            </ul>
          </li>
        </ul>
        <form action="" class="navbar-search pull-left">
          <input type="text" placeholder="Search" class="search-query span2">
        </form>
        <ul class="nav pull-right">
          <li><a href="#">Link</a></li>
          <li class="divider-vertical"></li>
          <li class="dropdown">
            <a class="#" href="#">Menu</a>
          </li>
        </ul>
      </div>
      <!-- /.nav-collapse -->
    </div>
  </div>
</div>

<hr>

<ul class="nav nav-pills">
  <li class="active"><a href="#">Regular link</a></li>
  <li class="dropdown">
    <a href="#" data-toggle="dropdown" class="dropdown-toggle">Dropdown <b class="caret"></b></a>
    <ul class="dropdown-menu" id="menu1">
      <li>
        <a href="#">2-level Menu <i class="icon-arrow-right"></i></a>
        <ul class="dropdown-menu sub-menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li class="nav-header">Nav header</li>
          <li><a href="#">Separated link</a></li>
          <li><a href="#">One more separated link</a></li>
        </ul>
      </li>
      <li><a href="#">Another action</a></li>
      <li><a href="#">Something else here</a></li>
      <li class="divider"></li>
      <li><a href="#">Separated link</a></li>
    </ul>
  </li>
  <li class="dropdown">
    <a href="#">Menu</a>
  </li>
  <li class="dropdown">
    <a href="#">Menu</a>
  </li>
</ul>