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来源：2-10 编程练习

慕沐7533447

2018-08-03 16:50:45

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
    /*完善下列代码*/
    .per{
     width: 300px;
     height: 300px;
     background: red;
     margin-left:200px;
     margin-top: 200px;
     position:relative;
   }   .son{
     width: 100px;
     height: 100px;
     background: blue;
     position:absolute;
     margin:auto;
     top:0;
     left:0;
     right:0;
     bottom:0;
   }
</style>
</head>
<body>
<div class="per">
    <div class="son"></div>
</div>
</body>
</html>