案例：CSS案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE HTML>
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<html>
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<head>
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<style type="text/css">
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h1 > strong {color:red;}
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</style>
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</head>
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​
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<body>
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<h1>This is <strong>very</strong> <strong>very</strong> important.</h1>
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<h1>This is <em>really <strong>very</strong></em> important.</h1>
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</body>
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</html>
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​