#portal {
  display: grid;
  place-content: center;
  text-align: center;
  color: white;
  font-size: min(20vh, 13vw);
  view-timeline: --portal;
}

#portal > span {
  position: sticky;
  top: calc(50% - min(20vh, 10vw) / 2);

  animation: portal-zoom ease-in;
  animation-range: 50%;
  animation-timeline: --portal;

  z-index: 2;  /* over #timber */
}

@keyframes portal-zoom {
  to {
    scale: 100;
  }
}