折叠 | Collapse
左側導航菜單 用panel-collapse
參考：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css">
</head>
<body>
<div class="container-fluid">
<div class="row">
<div class="col-md-2">
<ul id="main-nav" class="main-nav nav nav-tabs nav-stacked" style="">
<li>
<a href="#systemSetting" class="nav-header collapsed" data-toggle="collapse">
<i class="glyphicon glyphicon-cog"></i>
系统管理
<span class="pull-right glyphicon glyphicon-chevron-toggle"></span>
</a>
<ul id="systemSetting" class="nav nav-list secondmenu collapse" style="height: 0px;">
<li><a href="#"><i class="glyphicon glyphicon-user"></i> 用户管理</a></li>
<li><a href="#"><i class="glyphicon glyphicon-th-list"></i> 菜单管理</a></li>
<li><a href="#"><i class="glyphicon glyphicon-asterisk"></i> 角色管理</a></li>
<li><a href="#"><i class="glyphicon glyphicon-edit"></i> 修改密码</a></li>
<li><a href="#"><i class="glyphicon glyphicon-eye-open"></i> 日志查看</a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
<script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
</body>
</html>
在線運行：
http://www.runoob.com/try/try.php?filename=bootstrap3-plugin-dropdown-method
其他參考：
https://www.jb51.net/article/106487.htm
https://www.jb51.net/article/82980.htm
http://www.runoob.com/bootstrap/bootstrap-collapse-plugin.html