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我正在学习Bootstrap，但我可以使子菜单出现为什么子菜单不能在此Bootstrap模板上工作？
单击子菜单时，它没有响应。应该有子菜单下拉菜单。
这里，我试图复制bootsnipp.com/fullscreen/r1Pjd
所有来源是CDN原。
我该如何解决这个问题？
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
<!-- Latest compiled and minified CSS-->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<!-- Optional theme -->
<link rel="stylesheet" href="https://netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">
<link rel="stylesheet" href="https://bootsnipp.com/dist/bootsnipp.min.css" crossorigin="anonymouse">
<link href="//maxcdn.bootstrapcdn.com/font-awesome/4.2.0/css/font-awesome.min.css" rel="stylesheet">
<!-- Latest compiled and minified JavaScript -->
<style>
.nav-side-menu {
overflow: auto;
font-family: verdana;
font-size: 12px;
font-weight: 200;
background-color: #2e353d;
position: fixed;
top: 0px;
width: 300px;
height: 100%;
color: #e1ffff;
}
.nav-side-menu .brand {
background-color: #23282e;
line-height: 50px;
display: block;
text-align: center;
font-size: 14px;
}
.nav-side-menu .toggle-btn {
display: none;
}
.nav-side-menu ul,
.nav-side-menu li {
list-style: none;
padding: 0px;
margin: 0px;
line-height: 35px;
cursor: pointer;
/*
.collapsed{
.arrow:before{
font-family: FontAwesome;
content: "\f053";
display: inline-block;
padding-left:10px;
padding-right: 10px;
vertical-align: middle;
float:right;
}
}
*/
}
.nav-side-menu ul :not(collapsed) .arrow:before,
.nav-side-menu li :not(collapsed) .arrow:before {
font-family: FontAwesome;
content: "\f078";
display: inline-block;
padding-left: 10px;
padding-right: 10px;
vertical-align: middle;
float: right;
}
.nav-side-menu ul .active,
.nav-side-menu li .active {
border-left: 3px solid #d19b3d;
background-color: #4f5b69;
}
.nav-side-menu ul .sub-menu li.active,
.nav-side-menu li .sub-menu li.active {
color: #d19b3d;
}
.nav-side-menu ul .sub-menu li.active a,
.nav-side-menu li .sub-menu li.active a {
color: #d19b3d;
}
.nav-side-menu ul .sub-menu li,
.nav-side-menu li .sub-menu li {
background-color: #181c20;
border: none;
line-height: 28px;
border-bottom: 1px solid #23282e;
margin-left: 0px;
}
.nav-side-menu ul .sub-menu li:hover,
.nav-side-menu li .sub-menu li:hover {
background-color: #020203;
}
.nav-side-menu ul .sub-menu li:before,
.nav-side-menu li .sub-menu li:before {
font-family: FontAwesome;
content: "\f105";
display: inline-block;
padding-left: 10px;
padding-right: 10px;
vertical-align: middle;
}
.nav-side-menu li {
padding-left: 0px;
border-left: 3px solid #2e353d;
border-bottom: 1px solid #23282e;
}
.nav-side-menu li a {
text-decoration: none;
color: #e1ffff;
}
.nav-side-menu li a i {
padding-left: 10px;
width: 20px;
padding-right: 20px;
}
.nav-side-menu li:hover {
border-left: 3px solid #d19b3d;
background-color: #4f5b69;
-webkit-transition: all 1s ease;
-moz-transition: all 1s ease;
-o-transition: all 1s ease;
-ms-transition: all 1s ease;
transition: all 1s ease;
}
@media (max-width: 767px) {
.nav-side-menu {
position: relative;
width: 100%;
margin-bottom: 10px;
}
.nav-side-menu .toggle-btn {
display: block;
cursor: pointer;
position: absolute;
right: 10px;
top: 10px;
z-index: 10 !important;
padding: 3px;
background-color: #ffffff;
color: #000;
width: 40px;
text-align: center;
}
.brand {
text-align: left !important;
font-size: 22px;
padding-left: 20px;
line-height: 50px !important;
}
}
@media (min-width: 767px) {
.nav-side-menu .menu-list .menu-content {
display: block;
}
}
body {
margin: 0px;
padding: 0px;
}
</style>
</head>
<body>
<div class="nav-side-menu">
<div class="brand">Brand Logo</div>
<i class="fa fa-bars fa-2x toggle-btn" data-toggle="collapse" data-target="#menu-content"></i>
<div class="menu-list">
<ul id="menu-content" class="menu-content collapse out">
<li>
<a href="#">
<i class="fa fa-dashboard fa-lg"></i> Dashboard
</a>
</li>
<li data-toggle="collapse" data-target="#products" class="collapsed active">
<a href="#"><i class="fa fa-gift fa-lg"></i> UI Elements <span class="arrow"></span></a>
</li>
<ul class="sub-menu collapse" id="products">
<li class="active"><a href="#">CSS3 Animation</a></li>
<li><a href="#">General</a></li>
<li><a href="#">Buttons</a></li>
<li><a href="#">Tabs & Accordions</a></li>
<li><a href="#">Typography</a></li>
<li><a href="#">FontAwesome</a></li>
<li><a href="#">Slider</a></li>
<li><a href="#">Panels</a></li>
<li><a href="#">Widgets</a></li>
<li><a href="#">Bootstrap Model</a></li>
</ul>
<li data-toggle="collapse" data-target="#service" class="collapsed">
<a href="#"><i class="fa fa-globe fa-lg"></i> Services <span class="arrow"></span></a>
</li>
<ul class="sub-menu collapse" id="service">
<li>New Service 1</li>
<li>New Service 2</li>
<li>New Service 3</li>
</ul>
<li data-toggle="collapse" data-target="#new" class="collapsed">
<a href="#"><i class="fa fa-car fa-lg"></i> New <span class="arrow"></span></a>
</li>
<ul class="sub-menu collapse" id="new">
<li>New New 1</li>
<li>New New 2</li>
<li>New New 3</li>
</ul>
<li>
<a href="#">
<i class="fa fa-user fa-lg"></i> Profile
</a>
</li>
<li>
<a href="#">
<i class="fa fa-users fa-lg"></i> Users
</a>
</li>
</ul>
</div>
</div>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<script src="https://code.jquery.com/jquery-3.2.1.min.js"
integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4="
crossorigin="anonymous">
</script>
</body>
</html>
[bootsrap nav-bar collapsable可能重复无法使其工作]（https://stackoverflow.com/questions/38705798/bootsrap-nav-bar-collapsable-cannot-make-it-work） – vanburen