.wp-block-cover--mobile-image-img {
  display: none;
}

@media (max-width:768px) {

  .wp-block-cover__image-background  {
    z-index: 0 !important;
  }

  .wp-block-cover--mobile-image-img {
    display: block;
    z-index: 1 !important;
  }
}