Code:

<div id="mySidenav" class="sidenav">
    <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">&times;</a>
    <a href="#">About</a>
    <a href="#">Services</a>
    <a href="#">Clients</a>
    <a href="#">Contact</a>
</div>

<h2>侧边栏</h2>
<p>点击以下菜单图标打开侧边栏。</p>
<span style="font-size:30px;cursor:pointer" onclick="openNav()">&#9776; 打开</span>
<style>
    body {
        font-family: "Lato", sans-serif;
    }
    
    .sidenav {
        display: none;
        height: 100%;
        width: 250px;
        position: fixed;
        z-index: 1;
        top: 0;
        left: 0;
        background-color: #111;
        overflow-x: hidden;
        padding-top: 60px;
    }
    
    .sidenav a {
        padding: 8px 8px 8px 32px;
        text-decoration: none;
        font-size: 25px;
        color: #818181;
        display: block;
    }
    
    .sidenav a:hover, .offcanvas a:focus{
        color: #f1f1f1;
    }
    
    .sidenav .closebtn {
        position: absolute;
        top: 0;
        right: 25px;
        font-size: 36px;
        margin-left: 50px;
    }
    
    @media screen and (max-height: 450px) {
      .sidenav {padding-top: 15px;}
      .sidenav a {font-size: 18px;}
    }
</style>

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