.grid__image--has-secondary-img {
  position: relative;
}
.image--secondary {
  position: absolute;
  opacity: 0;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  transition: opacity 0.3s ease-in-out;
}
.grid__image--has-secondary-img:hover .image--secondary {
  opacity: 1;
}
.grid__image--has-secondary-img:hover .image--primary {
  opacity: 0;
}