button#mode {
  position: fixed;
  top: 1em;
  right: 0.9em;
  opacity: 0.5;
  transition: opacity 0.25, translate 0.25s;
  &:hover { opacity: 1 }
  &:active { translate: 1px 1px; }
  font-size: 2rem;
  z-index: 30;
  background: none;
  border: none;
}