Color Overlay on Hover for Image (NOT a gallery)

Hello!! I am looking to create a 50% opacity white hover effect on a few images (not a gallery). I tried to use this code but it doesn't work 🤨

.image-block {
    img {
      opacity: 1;

transition: .3s ease;
    }
   
    img:hover {
      opacity: .5;
    }
  }

Try this Custom CSS instead:

.image-block img {
  opacity: 1;
  transition: .3s ease;
}   
.image-block img:hover {
  opacity: 0.5;
}