我的垂直居中

如下：

<!DOCTYPE html>

<title>Signin Template for Bootstrap</title>

<link href="http://cdn.bootcss.com/bootstrap/3.3.2/css/bootstrap.min.css" rel="stylesheet">
    <style>
        .vertical-center {
            position: absolute;
            top: 40%;
            left: 50%;
            transform: translate(-50%, -50%);
        }
    </style>
</head>
<body>
    <div class="container vertical-center" style="border:1px solid blue;">
        <div class="col-lg-4 col-lg-offset-4 col-sm-6 col-sm-offset-3 col-xs-8 col-xs-offset-2" id="logindev" style="border:1px solid red;">
            <form class="form">
                <h2>Please sign in</h2>
                <label for="inputEmail" class="sr-only">Email address</label>
                <input type="email" id="inputEmail" class="form-control" placeholder="Email address" required="" autofocus="">
                <label for="inputPassword" class="sr-only">Password</label>
                <input type="password" id="inputPassword" class="form-control" placeholder="Password" required="">
                <div class="checkbox">
                    <label>
                        <input type="checkbox" value="remember-me"> Remember me
                    </label>
                </div>
                <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
            </form>
        </div>
    </div> 
</body>
</html>