// Center an element on the screen
(function($){
  $.fn.extend({
    center: function (x,y) {
      return this.each(function() {
                if (x == undefined) {
                    x = true;
                }
                if (y == undefined) {
                    y = true;
                }
                var $this = $(this);
                var $window = $(window);
                $this.css({
                    position: "absolute"
                });
                if (x) {
                    var left = ($window.width() - $this.outerWidth())/2+$window.scrollLeft();
                    $this.css('left',left)
                }
                if (!y == false) {
                var top = ($window.height() - $this.outerHeight())/2+$window.scrollTop();   
                    $this.css('top',top);
                }
        return $(this);
      });
    }
  });
})(jQuery);