.snow {
    position: absolute;
    left: -100px;
    right: -100px;
    animation: wind 5s cubic-bezier(0.51, 0.01, 0.63, 0.99) infinite alternate;
    opacity: 0.4;
    z-index: -1;
}

.snow::after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    min-height: 2000px;
    background: url(../pictures/snow.png);
    animation: fall 10s linear infinite;
}

@keyframes fall {
    from {
        transform: translateY(-1000px);
    }
}

@keyframes wind {
    to {
        transform: translateX(50px);
    }
}