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代码编辑器：

<!DOCTYPE html>
<meta charset="utf-8">
<link href="/static/next/css/tryit.css?v=2017082407" rel="stylesheet"/>
<style>
.dropbtn {
    background-color: #4CAF50;
    color: white;
    padding: 16px;
    font-size: 16px;
    border: none;
    cursor: pointer;
}
.dropdown {
    position: relative;
    display: inline-block;
}
.dropdown-content {
    display: none;
    position: absolute;
    right: 0;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}
.dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
}
.dropdown-content a:hover {background-color: #f1f1f1}
.dropdown:hover .dropdown-content {
    display: block;
}
.dropdown:hover .dropbtn {
    background-color: #3e8e41;
}
</style>
<h2>下拉内容的对齐方式</h2>
<p>left 和 right 属性指定了下拉内容是从左到右或从右到左。</p>
<div class="dropdown" style="float:left;">
  <button class="dropbtn">左</button>
  <div class="dropdown-content" style="left:0;">
    <a href="#">简单教程 1</a>
    <a href="#">简单教程 2</a>
    <a href="#">简单教程 3</a>
  </div>
</div>
<div class="dropdown" style="float:right;">
  <button class="dropbtn">右</button>
  <div class="dropdown-content">
    <a href="#">简单教程 1</a>
    <a href="#">简单教程 2</a>
    <a href="#">简单教程 3</a>
  </div>
</div>
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