@keyframes snowfall {
    0% {
        transform: translate3d(var(--left-start), 0, 0) rotate(0);
    }

    100% {
        transform: translate3d(var(--left-end), 100vh, 0) rotate(var(--rotate));
    }
}

.snow {
    position: fixed;
    user-select: none;
    color: lightskyblue;
    --left-start: 0;
    --left-end: 0;
    --rotate: 360deg;
    z-index: 99999;
}