.row {
  position: relative;
  width: 100%;
  display: flex;
  justify-content: space-around;
}

.image-link {
  display: flex;
  width: 100%;
  text-decoration: none;
}

.thumbnail {
  width: 33%; 
  height: auto;
}

.overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  opacity: 0;
  transition: opacity .3s;
  background: rgba(0,0,0,0.6);
}

.title {
  color: white;
  font-size: 2em;
}

.image-link:hover .overlay {
  opacity: 1;
}