.thumbnail {
  position: relative;
  width: 200px;
  height: 200px;
  overflow: hidden;
}

.thumbnail img {
  position: absolute;
  left: 50%;
  top: 50%;
  height: 100%;
  width: auto;
  transform: translate(-50%,-50%);
}

.thumbnail img.portrait {
  width: 100%;
  height: auto;
}