text: var coll = document.getElementsByClassName("collapsible");
  
  for (var i = 0; i < coll.length; i++)
  {
    coll[i].addEventListener("click", function ()
    {
      this.classList.toggle("active");
      var content = this.nextElementSibling;
      if (content.style.maxHeight)
      {
        content.style.maxHeight = null;
      }
      else
      {
        content.style.maxHeight = content.scrollHeight + "px";
      }
    });
  
    // expand by default
    var content = coll[i].nextElementSibling;
    content.style.maxHeight = content.scrollHeight + "px";
    coll[i].classList.toggle("active");
  }
  