index.js

this.$palettes.on('hidden.bs.collapse', function (e) {
      var $this = $(this),
        $target = $(e.target),
        targetPage = $target.attr('id').slice(0, -6);

      var $i = $("span[itemprop=expandCollapseIcons] i", $(targetPage + "-panel"));
      if ($i.hasClass('icon-chevron-down')) {
        $i.removeClass('icon-chevron-down').addClass('icon-chevron-up');
      } else {
        $i.removeClass('icon-chevron-up').addClass('icon-chevron-down');
      }



    });

    this.$palettes.on('show.bs.collapse', function (e) {
      var iframe = self.iframe(),
        $iframe = $(iframe.document),
        $this = $(this),
        $target = $(e.target),
        targetPage = $target.attr('id').slice(0, -6);


      var $i = $("span[itemprop=expandCollapseIcons] i", $(targetPage + "-panel"));
      if ($i.hasClass('icon-chevron-up')) {
        $i.removeClass('icon-chevron-up').addClass('icon-chevron-down');
      } else {
        $i.removeClass('icon-chevron-down').addClass('icon-chevron-up');
      }