.jarallax {
    position: relative;
    z-index: 0;
}
.jarallax > .jarallax-img {
  position: absolute;
  object-fit: contain; /* show full image */
  font-family: 'object-fit: contain;';
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
  background-color: #000; /* optional: fill empty space with black */
}