<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
html,
body {
height: 100%;
}
body {
width: 100%;
position: relative;
}
div {
width: 200px;
height: 200px;
background-color: #f00;
position: absolute;
top: 50%;
left: 50%;
margin-top: -100px;
margin-left: -100px;
}
</style>
</head>
<body>
<div>
</div>
</body>
</html>
效果：上下左右都居中
写一个200宽高的div，上下左右居中
原文：https://www.cnblogs.com/Friday1/p/14709353.html
