body #content0 button {
  appearance: none;
  border: 1px solid;
  font-weight: bold;
  background-color: white;
  padding: 1em 2em;
  margin-top: 3em;
  width: auto;
  opacity: 1;
  color: black;
  position: absolute;
  bottom: 2em;
  left: 2em;
  right: 2em;
}
body[step=step0] #content0 {
  transition: opacity 500ms ease, transform 500ms ease, z-index 0ms ease 0ms;
  z-index: 2;
  opacity: 1;
  transform: translate3d(0, 0, 0);
}
body:not([step=step0]) #content0 {
  transition: opacity 250ms ease, transform 250ms ease, z-index 0ms ease 500ms;
  z-index: -1;
  opacity: 0;
  transform: translate3d(0, 2em, 0);
}