document.addEventListener('DOMContentLoaded', function() {
  var headers = document.querySelectorAll('h4');

  headers.forEach(function(header) {
    header.addEventListener('click', function() {
      var nextElement = header.nextElementSibling;
      if (nextElement) {
        var collapsibleList = nextElement.querySelector('.playlist, .notes, .contents');
        if (collapsibleList) {
          header.classList.toggle('active');
          collapsibleList.classList.toggle('active');
        }
      }
    });
  });
});