案例：javascript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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body
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{
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background-color:#FFCC80;
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background-image:url(/img/eg_bg_desert.jpg);
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background-repeat:no-repeat;
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background-attachment:fixed;
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}
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</style>
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<script type="text/javascript">
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function changePosition()
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{
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document.body.style.backgroundPositionY="bottom";
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}
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</script>
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</head>
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<body>
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​
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<input type="button" onclick="changePosition()" value="Change background-image's y-position" />
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<p><b>Note:</b> For this to work in Mozilla, the background-attachment property must be set to "fixed".</p>
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</body>
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</html>
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​