.bg-slideshow {
  position: fixed;
  inset: 0;
  z-index: -1;
  background: #111;
}
.bg-slideshow img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  opacity: 0;
  transition: opacity 2s ease-in-out;
}
.bg-slideshow img.active { opacity: 1; }