#fog {
        height: 100%;
        width: 100%;
        background-repeat: repeat;
        background-image: url("Image/Others/fog.png");
        position: absolute;
        opacity: 0;
        pointer-events: none;
        z-index: 99999
       }

#fog.animation {
    animation: fog 2s ease-in-out forwards
}
@keyframes fog {
        0% {
            opacity: 0
        }
        100% {
            opacity: 0.99
        } 
    }