.bg-image {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-size: cover;
    background-position: center;
    opacity: 0;
    pointer-events: none;
    transition: none;
    z-index: -2;
}
.bg-image.show {
    z-index: -1;
    animation: fadeIn 1s ease-in-out forwards;
}
@keyframes fadeIn {
    0% { opacity: 0; }
    100% { opacity: 1; }
}