Bootstrap3 添加下拉菜单的子菜单 dropdown-submenu

bootstrap3-dropdown-submenu.css

.dropdown-submenu  { 
    position:relative;
}
.dropdown-submenu > .dropdown-menu { 
    top:0;
    left:100%;
    margin-top:-6px;
    margin-left:-1px;
    -webkit-border-radius:0 6px 6px 6px;
    -moz-border-radius:0 6px 6px 6px;
    border-radius:0 6px 6px 6px;
}
.dropdown-submenu:hover > .dropdown-menu { 
    display:block;
}
.dropdown-submenu > a:after { 
    display:block;
    content:" ";
    float:right;
    width:0;
    height:0;
    border-color:transparent;
    border-style:solid;
    border-width:5px 0 5px 5px;
    border-left-color:#cccccc;
    margin-top:5px;
    margin-right:-10px;
}
.dropdown-submenu:hover > a:after { 
    border-left-color:#ffffff;
}
.dropdown-submenu.pull-left { 
    float:none;
}
.dropdown-submenu.pull-left > .dropdown-menu { 
    left:-100%;
    margin-left:10px;
    -webkit-border-radius:6px 0 6px 6px;
    -moz-border-radius:6px 0 6px 6px;
    border-radius:6px 0 6px 6px;
}

demo.html

<ul class="dropdown-menu" role="menu" aria-labelledby="dLabel">
  ...
  <li class="dropdown-submenu">
    <a tabindex="-1" href="#">More options</a>
    <ul class="dropdown-menu">
      ...
    </ul>
  </li>
</ul>