代码编辑器：
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<style>3
[class|=top]4
{5
background:yellow;6
}7
</style>8
<h1 class="top-header">Welcome</h1>9
<p class="top-text">Hello world!</p>10
<p class="content">Are you learning CSS?</p>11
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<p><b>Note:</b> For [<i>attribute</i>|=<i>value</i>] to work in IE8 and earlier, a DOCTYPE must be declared.</p>13
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<footer>简单教程，简单编程<br/>Copyright © 简单教程 www.twle.cn</footer>15