gistfile1.js

$(function () {
  $('#page').append($("<div class='bg'></div>"));
});

$(window).scroll(function (e) {
  parallax();
});

function parallax() {
  var scrolled = $(window).scrollTop();
  var list_1 = parseInt($('.list_left1').css('top'));
  
  $('#bg').css('top', -(scrolled * 0.2) + 'px');
  $('#bg').css('top', list_1 + (scrolled * 0.3) + 'px');
}