#unterbild {
  width: 50%;
  height: 20rem;
  place-self: start;
}
#unterbild img {
  width: 70%;
  height: 80%;
  place-self: end;
  object-position: left;
}

@media (max-width: 750px) {
  #unterbild,
  #unterbild img {
    width: 100%;
    height: 100%;
  }
}