简单教程
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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> /* For width smaller than 400px: */ body { background-repeat: no-repeat; background-image: url('/static/i/css/img_smallflower.jpg'); } /* For width 400px and larger: */ @media only screen and (min-width: 400px) { body { background-image: url('/static/i/css/img_flowers.jpg'); } } </style> <p style="margin-top:360px;">调整浏览器宽度，背景图片在小于 400 px 时将改变。</p> <footer>简单教程，简单编程<br/>Copyright © 简单教程 www.twle.cn</footer>
运行结果：