This question has been answered by BobRay. See the first response.
$(document).ready(function() { $.fn.slideFadeToggle = function(speed, easing, callback) { return this.animate({opacity: 'toggle', height: 'toggle'}, speed, easing, callback); }; $('.accordion').accordion({ //defaultOpen: 'open', speed: 'fast', animateOpen: function (elem, opts) { elem.children(":first").removeClass('fa fa-angle-down'); elem.children(":first").toggleClass('fa fa-angle-up'); elem.next().stop(true, true).slideFadeToggle(opts.speed); }, animateClose: function (elem, opts) { elem.children(":first").removeClass('fa fa-angle-up'); elem.children(":first").toggleClass('fa fa-angle-down'); elem.next().stop(true, true).slideFadeToggle(opts.speed); } }); });