document.addEventListener('DOMContentLoaded', function () {
  // 'Back to top' logic
  const intersectionObserver = new IntersectionObserver(function(entries) {
    const topBtn = document.querySelector('.top-of-site-link');
    if (topBtn === null) return;

    topBtn.dataset.visible = entries[0].boundingClientRect.y < 0;
  });

  const topAnchor = document.querySelector('#top-of-site-anchor');
  if (topAnchor !== null) {
    intersectionObserver.observe(topAnchor);
  }
});