JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<div class="navbar">
  <div class="navbar-inner">
      <ul class="nav">
          <li class="dropdown">
              <a data-toggle="dropdown" class="dropdown-toggle" href="#">Dropdown <b class="caret"></b></a>
               <ul class="dropdown-menu">
                    <li>
                    <a href="#" style="overflow: hidden;">
                        <span class="pull-left">2-level Dropdown</span>
                        <span class="icon-arrow-right pull-right"></span>
                    </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>
                    </ul>
                </li>
                <li><a href="#">Another action</a></li>
                <li class="divider"></li>
                <li><a href="#">One more separated link</a></li>
              </ul>
            </li>
          </ul>
  </div>
</div>

CSS

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;
}