.slider-bg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: 0;
    transition: opacity 1s ease-in-out;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
}
.slider-bg.active {
    opacity: 1;
}