div 垂直水平居中在父元素中间

<html>
<style>
body{
background-color:#ccc;
height:100%;
position:relative;
}
.login{
width:500px;
height:600px;
border:1px solid #fff;
background:rgba(255,255,255,0.3);
position:absolut;
top:50%;
height:50%;
margin-left:250px;
margin-top:300px;
/*
transform:tranlate(25%,30%);
*/
}
</style>
<body>
<div class="login"></div>
</body>
<html>