body {
    margin: 0px;
}
div#screen {
    width: 640px;
    height: 480px;
    position: relative;
    border-radius: 20px;
    overflow: hidden;
    z-index: 1;
}
.center{
    width: 640px;
    margin: auto;
    padding: 20px;
}
.center2{
    display: flex;
    justify-content: center;
}