(function ($) {
    $.fn.center = function () {
        this.css("display", "block");
        this.css("top", ($(window).height() - this.height()) / 2 + $(window).scrollTop() + "px");
        this.css("left", ($(window).width() - this.width()) / 2 + $(window).scrollLeft() + "px");
        return this;
    }

    $.fn.center_iframe = function () {
        this.css("display", "block");
        this.css("top", ($(document).height() - this.height()) / 2 + $(document).scrollTop() + "px");
        this.css("left", ($(document).width() - this.width()) / 2 + $(document).scrollLeft() + "px");
        return this;
    }
})(jQuery);