页面的head部分，需远程调用bootstrap样式库和font-awesome图标字体库，并引入本地样式文件，代码如下：

<link type="text/css" rel="stylesheet" href="http://apps.bdimg.com/libs/bootstrap/3.3.4/css/bootstrap.css">
<link type="text/css" rel="stylesheet" href="http://cdn.bootcss.com/font-awesome/4.6.0/css/font-awesome.min.css">
<link type="text/css" rel="stylesheet" href="css/bootsnav.css">
<style type="text/css">
body{ background-color:hsla(0,0%,18%,1.00)}
.header h1{ text-align:center; font-size:28px; color:#939393}
.navbar-brand{
    padding: 29px 15px;
    height: auto;
}
nav.navbar.bootsnav{
    border: none;
    margin-bottom: 150px;
}
.navbar-nav{
    float: left;
}
nav.navbar.bootsnav ul.nav > li > a{
    color: #474747;
    text-transform: uppercase;
    padding: 30px;
}
nav.navbar.bootsnav ul.nav > li:hover{
    background: #f4f4f4;
}
.nav > li:after{
    content: "";
    width: 0;
    height: 5px;
    background: #34c9dd;
    position: absolute;
    bottom: 0;
    left: 0;
    transition: all 0.5s ease 0s;
}
.nav > li:hover:after{
    width: 100%;
}
nav.navbar.bootsnav ul.nav > li.dropdown > a.dropdown-toggle:after{
    content: "+";
    font-family: 'FontAwesome';
    font-size: 16px;
    font-weight: 500;
    position: absolute;
    top: 35%;
    right: 10%;
    transition: all 0.4s ease 0s;
}
nav.navbar.bootsnav ul.nav > li.dropdown.on > a.dropdown-toggle:after{
    content: "\f105";
    transform: rotate(90deg);
}
.dropdown-menu.multi-dropdown{
    position: absolute;
    left: -100% !important;
}
nav.navbar.bootsnav li.dropdown ul.dropdown-menu{
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.3);
    border: none;
}
@media only screen and (max-width:990px){
    nav.navbar.bootsnav ul.nav > li.dropdown > a.dropdown-toggle:after,
    nav.navbar.bootsnav ul.nav > li.dropdown.on > a.dropdown-toggle:after{ content: " "; }
    .dropdown-menu.multi-dropdown{ left: 0 !important; }
    nav.navbar.bootsnav ul.nav > li:hover{ background: transparent; }
    nav.navbar.bootsnav ul.nav > li > a{ margin: 0; }
}
</style>

页面的body部分，用了多个div的嵌套结构来放入多级菜单的内容，代码如下：

<div class="demo" style="padding: 2em 0;">
	<div class="container">
		<div class="row">
			<div class="col-md-12">
				<nav class="navbar navbar-default navbar-mobile bootsnav">
					<div class="navbar-header">
						<button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#navbar-menu">
							<i class="fa fa-bars"></i>
						</button>
					</div>
					<div class="collapse navbar-collapse" id="navbar-menu">
						<ul class="nav navbar-nav" data-in="fadeInDown" data-out="fadeOutUp">
							<li><a href="#">Home</a></li>
							<li><a href="#">About Us</a></li>
							<li class="dropdown">
								<a href="#" class="dropdown-toggle" data-toggle="dropdown">Shortcodes</a>
								<ul class="dropdown-menu">
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li class="dropdown">
										<a href="#" class="dropdown-toggle" data-toggle="dropdown" >Sub Menu</a>
										<ul class="dropdown-menu">
											<li><a href="#">Custom Menu</a></li>
											<li><a href="#">Custom Menu</a></li>
											<li class="dropdown">
												<a href="#" class="dropdown-toggle" data-toggle="dropdown" >Sub Menu</a>
												<ul class="dropdown-menu multi-dropdown">
													<li><a href="https://jy.tp.yuanmeng.life/">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
												</ul>
											</li>
											<li><a href="#">Custom Menu</a></li>
										</ul>
									</li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
								</ul>
							</li>
							<li class="dropdown">
								<a href="#" class="dropdown-toggle" data-toggle="dropdown">Pages</a>
								<ul class="dropdown-menu">
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li class="dropdown">
										<a href="#" class="dropdown-toggle" data-toggle="dropdown">Sub Menu</a>
										<ul class="dropdown-menu">
											<li><a href="#">Custom Menu</a></li>
											<li><a href="#">Custom Menu</a></li>
											<li class="dropdown">
												<a href="#" class="dropdown-toggle" data-toggle="dropdown">Sub Menu</a>
												<ul class="dropdown-menu multi-dropdown">
													<li><a href="#">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
													<li><a href="#">Custom Menu</a></li>
												</ul>
											</li>
											<li><a href="#">Custom Menu</a></li>
										</ul>
									</li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
									<li><a href="#">Custom Menu</a></li>
								</ul>
							</li>
							<li><a href="#">Portfolio</a></li>
							<li><a href="#">Contact Us</a></li>
						</ul>
					</div>
				</nav>
			</div>
		</div>
	</div>
</div>

页面的底部，需引入jQuery和bootstrap库、bootsnav.js文件，代码如下：

<script type="text/javascript" src="js/jquery.min.js"></script>
<script type="text/javascript" src="js/bootstrap.min.js"></script>
<script type="text/javascript" src="js/bootsnav.js"></script>