.fullscreen {
  color: #818181;
  text-align: end;
  font-size: 2rem;
  margin-bottom: 1rem;
}

  height: 6rem;

  height: 6.5rem;

  height: 90vw;

  height: 82vw;

  fullscreen_button.addEventListener("click", (e) => {
    const element = document.body;
    if (document.fullscreenElement == null) {
      element.requestFullscreen();
    } else {
      document.exitFullscreen();
    }
  });

      <div id="fullscreen_button" class="fullscreen">⛶&nbsp;</div>