Bluesky：浮动的「回到顶部」按钮

// Floating "scroll to top" button appears after you scroll down
(function () {
  if (document.getElementById('jz-bsk-scrolltop')) { return; }
  var btn = document.createElement('button');
  btn.id = 'jz-bsk-scrolltop';
  btn.type = 'button';
  btn.textContent = '↑';
  btn.style.cssText = [
    'position:fixed', 'right:24px', 'bottom:24px', 'z-index:99999',
    'width:44px', 'height:44px', 'border-radius:50%',
    'border:0', 'background:#0085ff', 'color:#fff',
    'font-size:22px', 'cursor:pointer',
    'box-shadow:0 4px 16px rgba(0,0,0,0.25)',
    'display:none'
  ].join(';');
  btn.addEventListener('click', function () {
    window.scrollTo({ top: 0, behavior: 'smooth' });
  });
  document.body.appendChild(btn);
  function toggle() {
    btn.style.display = (window.scrollY > 600) ? 'block' : 'none';
  }
  toggle();
  window.addEventListener('scroll', toggle, { passive: true });
})();