固定寬高的div在瀏覽器居中（cvte在線測評） 和單行文字居中，
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>center</title>
</head>
<style>
#center{
position:absolute;
width:400px;
height:300px;
background:#ff0;
top:calc(50% - 150px);
left:calc(50% - 200px);
text-align:center;
line-height:300px;
}
</style>
<body>
<div id="center">單行文字居中</div>
</body>
</html>第二種
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>第二種垂直居中</title>
</head>
<style>
#wrapper{
position:absolute;
top:0;
bottom:0;
left:0;
right:0;
margin:auto;
height:240px;
width:70%;
background:blue;
}
</style>
<body>
<div id="wrapper">456
</div>
</body>
</html>