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代码编辑器：
<!DOCTYPE html> <style> [class|=top] { background:yellow; } </style> <h1 class="top-header">Welcome</h1> <p class="top-text">Hello world!</p> <p class="content">Are you learning CSS?</p> <p><b>Note:</b> For [<i>attribute</i>|=<i>value</i>] to work in IE8 and earlier, a DOCTYPE must be declared.</p> <footer>简单教程，简单编程<br/>Copyright © 简单教程 www.twle.cn</footer>
运行结果：