固定宽高块在浏览器中垂直居中
代码如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Demo</title>
<style>
html,body {
height: 100%;
}
#box {
position:absolute;
left:50%;
top:50%;
margin-left:-150px;
margin-top:-100px;
border:1px solid red;
background: #272626;
width:300px;
height:200px;
}
</style>
</head>
<body>
<div id = "box">
</div>
</body>
</html>
