$(function(){
    var backbutton = $('#btn-back-to-top');
    backbutton.hide();
    $(window).scroll(function () {
        if ($(this).scrollTop() > 100) {
            backbutton.fadeIn();
        } else {
            backbutton.fadeOut();
        }
    });
    backbutton.click(function () {
       $('body, html').animate({ scrollTop: 0 }, 500);
       return false;
    });
  });