@keyframes flip_card {
    0% {
        transform: rotateX(0deg);
    }
    49% {
        transform: rotateX(90deg);
    }
    51% {
        transform: rotateX(90deg);
    }
    100% {
        transform: rotateX(0deg);
    }
}

@keyframes next_card {
    0% {
        opacity: 1;
        transform: translateX(0);
    }
    49% {
        opacity: 0;
        transform: translateX(-100px);
    }
    51% {
        opacity: 0;
        transform: translateX(100px);
    }
    100% {
        opacity: 1;
        transform: translateX(0);
    }
}