<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
body,
html {
margin: 0;
width: 100%;
height: 100%;
}
#box {
width: 100%;
height: 100%;
background: rgba(0, 0, 0, 0.7);
position: relative;
}
#content {
position: absolute;
width: 70%;
height: 70%;
background: pink;
left: 50%;
top: 50%;
transform: translateX(-50%) translateY(-50%);
-ms-transform: translateX(-50%) translateY(-50%);
-webkit-transform: translateX(-50%) translateY(-50%);
}
</style>
</head>
<body>
<div id="box">
<div id="content"></div>
</div>
</body>
</html>
原文：https://www.cnblogs.com/dog2016/p/13168534.html