css3 transform实现水平和垂直居中

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>Document</title>
    <style>
        html, body {
        height: 100%;
        }
        .wrapper {
            position: relative;
            width: 100%;
            height: 100%;
            background: url("background.jpg") center no-repeat;
            background-size: cover;
        }

        .wrapper .login {
            position: absolute;
            width: 255px;
            height: 300px;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            background-color: #eee;
        }
    </style>
</head>
<body>
    <div class="wrapper">
        <div class="login"></div>
    </div>
</body>
</html>