.page {
    width: 100%;
    height: 100vh;
    position: absolute;
    top: 0;
    left: 0;
    background: rgba(255,255,255,0.9);
    border: 1px solid #ccc;
    overflow: hidden;
    transform-origin: top;
    transform: perspective(600px) rotateX(0deg);
    transition: transform 1s;
}

.next {
    transform: perspective(600px) rotateX(-90deg);
}