背景图像定位
如果背景图像不进行重复，你可以使用background-position属性来指定背景图像在浏览器窗口中的位置。这个位置可以随便变换。
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background-image: url("tulip.gif");
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background-position: center center;
color: #665544;
padding: 20px;}
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<h1>Planting Guide</h1>
<h2>Magnolia</h2>
<p><b><i>Magnolia grandiflora</i></b>, commonly known as the <b>Southern magnolia</b> or <b>bull bay</b>, is a tree of the family Magnoliaceae native to the southeastern United States, from coastal Virginia south to central Florida, and west to eastern Texas and Oklahoma. Reaching 27.5 m (90 ft) in height, it is a large striking evergreen tree with large dark green leaves and large white fragrant flowers. Widely cultivated around the world, over a hundred cultivars have been bred and marketed commercially. The timber is hard and heavy, and has been used commercially to make furniture, pallets, and veneer.</p>
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