.fog {
    position: absolute;
    z-index: 1;
    bottom: 0;
    left: 0;
    width: 250.625em;
    height: 243.75em;
    -webkit-animation: cloudLoop 80s linear infinite;
    animation: cloudLoop 80s linear infinite;
}

@keyframes cloudLoop {
    0% {
        -webkit-transform: translate3d(0, 0, 0);
        transform: translate3d(0, 0, 0);
    }
    100% {
        -webkit-transform: translate3d(-50%, 0, 0);
        transform: translate3d(-50%, 0, 0);
    }
}