方法1：
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.parent { width:800px; height:500px; border:2px solid #000; position:relative;} .child { width:200px; height:200px; margin: auto; position: absolute; top: 0; left: 0; bottom: 0; right: 0; background-color: red;} |
方法2：
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.parent { width:800px; height:500px; border:2px solid #000; display:table-cell; vertical-align:middle; text-align: center; } .child { width:200px; height:200px; display:inline-block; background-color: red; } |
方法3：
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.parent { width:800px; height:500px; border:2px solid #000; display:flex; justify-content:center; align-items:center; } .child { width:200px; height:200px; background-color: red; } |
方法4：
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.parent { width:800px; height:500px; border:2px solid #000; position:relative; } .child { width:300px; height:200px; margin:auto; position:absolute;/*设定水平和垂直偏移父元素的50%，再根据实际长度将子元素上左挪回一半大小*/ left:50%; top:50%; margin-left: -150px; margin-top:-100px; background-color: red; } |
原文：https://www.cnblogs.com/bydzhangxiaowei/p/9073517.html