案例:CSS3 案例     状态:可编辑再运行    进入竖版
 运行结果 
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<html>
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<head>
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<style type="text/css">
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h1 {letter-spacing: -0.5em}
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h4 {letter-spacing: 20px}
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</style>
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</head>
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<body>
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<h1>This is header 1</h1>
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<h4>This is header 4</h4>
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</body>
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</html>
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