.overlay {
  background-size: cover;
  background-position: center center;
  background-repeat: no-repeat;
}
.overlay a {
  background: linear-gradient(to bottom, rgba(0,0,0,0.5), rgba(0,0,0,0));  
  transition: background 0.3s;
  display: block;
  top: 0; left: 0; right: 0; bottom: 0;
  position: absolute;
}

.overlay a:hover {
  background: linear-gradient(to bottom, rgba(0,0,0,0.5), rgba(0,0,0,0.3) 15%, rgba(0,0,0,0));
}
.overlay h2 {
  margin:0;
  padding: 0.5rem 0;
  text-align: center;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  color: #fff;
}

.overlay nav {
  position: absolute;
  bottom: 0.5rem;
  right: 0.5rem;
}