.snow-bg {
    position: relative;
}

.snow-bg:after {
    content: '';
    display: block;
    position: absolute;
    z-index: 2;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    pointer-events: none;
    background-image: url('../images/s1.png'), url('../images/s2.png'), url('../images/s3.png');
    animation: snow 10s linear infinite;
}

@keyframes snow {
    0% {
        background-position: 0px 0px, 0px 0px, 0px 0px;
    }

    50% {
        background-position: 500px 500px, 100px 200px, -100px 150px;
    }

    100% {
        background-position: 500px 1000px, 200px 400px, -100px 300px;
    }
}