.html, body {
    width: 100vw;
    height: 100vh;
}

.precenter-vertically {
    -webkit-transform-style: preserve-3d;
    -moz-transform-style: preserve-3d;
    transform-style: preserve-3d;
}

.center-vertically {
    position: relative;
    top: 50%;
    transform: translateY(-50%);
}

.outer-wrapper {
    position: relative;
    width: 100%;
    height: 100vh;
}

.main-wrapper {
    width: 600px;
    margin: 0 auto;
}