body {background-size: 100%;}

h1 {color:black; text-align:center; font-size:50px}

div {
    height: 200px;
    width: 400px;
    background: none;

    position: fixed;
    top: 50%;
    left: 50%;
    margin-top: -100px;
    margin-left: -200px;
}

.center {
    margin: 0;
    padding:0;
    text-align: center;
    position: absolute;
    top: 50%;
    left:50%;
    transform: translateX(-50%) translateY(-50%);
}