<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge, chrome=1">
<meta name="format-detection" content="telephone=no" />
<title>扫一扫</title>
<style>
*{
margin:0;
padding:0;
}
.box{
width:800px;
height:800px;
margin:50px auto;
background-color: #ffff00;
}
.boc{
width:300px;
height:300px;
border: 500px solid rgba(0,0,0,0.5);
position: absolute;
left:0;
top:0;
right:0;
bottom:0;
margin:auto;
}
</style>
</head>
<body>
<div class="box">
<div class="boc"></div>
</div>
</body>
</html>
