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代码编辑器：

<!DOCTYPE html>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta charset="utf-8"><link href="/static/next/css/tryit.css?v=2017082407" rel="stylesheet"/>
 
<style>
.wrapper {overflow:auto;}

#main {margin-left: 4px;}
#leftsidebar {float: none;width: auto;}
#menulist {margin:0;padding:0;}

.menuitem {
    background:#CDF0F6;
    border:1px solid #d4d4d4;
    border-radius:4px;
    list-style-type:none;
    margin:4px;
    padding:2px;
}

@media screen and (min-width: 480px) {
    #leftsidebar {width:200px;float:left;}
    #main {margin-left:216px;}
}
</style>

<div class="wrapper">
  <div id="leftsidebar">
    <ul id="menulist">
      <li class="menuitem">Menu-item 1</li>
      <li class="menuitem">Menu-item 2</li>
      <li class="menuitem">Menu-item 3</li>
      <li class="menuitem">Menu-item 4</li>
      <li class="menuitem">Menu-item 5</li>
   </ul>
  </div>
  <div id="main">
    <h1>重置浏览器窗口查看效果！</h1>
    <p>在屏幕可视窗口尺寸大于 480 像素时将菜单浮动到页面左侧。</p>
  </div>
</div>
<footer>简单教程，简单编程<br/>Copyright © 简单教程 www.twle.cn</footer>

代码编辑器：

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