#nach-oben-button {
  position: fixed;
  right: 4rem;
  bottom: 4rem;
  transition: opacity 0.5 ease-in-out;
  opacity: 0;
  z-index: 100;
}

#nach-oben-button.show {
  opacity: 1;
}

@media screen and (max-width: 760px) {
  #nach-oben-button {
    right: 2rem;
    bottom: 2rem;
  }
}