(function () {
  const btn = document.createElement('button');
  btn.id = 'fsBtn';
  btn.textContent = '⛶';
  btn.title = 'Follscreen';
  btn.style.cssText = `
    position: fixed;
    top: 0.75rem;
    right: 0.75rem;
    z-index: 99999;
    background: transparent;
    border: none;
    color: rgba(255,255,255,0.1337);
    font-size: 1.25rem;
    cursor: pointer;
    padding: 0.25rem 0.5rem;
    transition: color 0.2s;
  `;
  btn.onmouseenter = () => btn.style.color = 'rgba(255,255,255,0.42)';
  btn.onmouseleave = () => btn.style.color = 'rgba(255,255,255,0.1337)';
  btn.onclick = () => {
    if (!document.fullscreenElement) {
      document.documentElement.requestFullscreen();
      btn.textContent = '✕';
    } else {
      document.exitFullscreen();
      btn.textContent = '⛶';
    }
  };
  document.addEventListener('fullscreenchange', () => {
    btn.textContent = document.fullscreenElement ? '✕' : '⛶';
  });
  document.body.appendChild(btn);
})();