(function($){
     $.fn.extend({
          center: function () {
                return this.each(function() {

                        var left = ($(window).width() - $(this).outerWidth()) / 2;
                        $(this).css({position:'absolute', margin:0, top: (top > 0 ? top : 0)+'px', left: (left > 0 ? left : 0)+'px'});
                });
        }
     });
})(jQuery);