position定位的上下左右居中
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<div class="yi">
<div class="er"></div>
</div>
</body>
</html>
<style>
.yi{
height:500px;
width:500px;
background:pink;
margin:30px auto;
position: relative;
}
.er{
height:200px;
width:200px;
background: #008000;
position: absolute;
top:50%;
left:50%;
transform: translate(-50%, -50%);
}
</style>
原文：https://www.cnblogs.com/xiaoyaolang/p/13275023.html