text: $(function() {
    var child_prefix = "l_";
    var parent_prefix = "h_";
  
    /* close up top-category */
    $(".collapse").on("hide.bs.collapse", function() { /* Bootstrap collapse events. */
      var parent_id = parent_prefix + $(this).attr('id').substring(child_prefix.length);
      if (parent_id) {
        $("#" + parent_id + " .far.fa-folder-open").attr("class", "far fa-folder fa-fw");
        $("#" + parent_id + " i.fas").addClass("rotate");
        $("#" + parent_id).removeClass("hide-border-bottom");
      }
    });
  
    /* expand the top category */
    $(".collapse").on("show.bs.collapse", function() {
      var parent_id = parent_prefix + $(this).attr('id').substring(child_prefix.length);
      if (parent_id) {
        $("#" + parent_id + " .far.fa-folder").attr("class", "far fa-folder-open fa-fw");
        $("#" + parent_id + " i.fas").removeClass("rotate");
        $("#" + parent_id).addClass("hide-border-bottom");
      }
    });
  
  });