pop.js

$(document).ready(function () {
    //open popup
    $(".pop").click(function () {
        $(this).parent().find("form .overlay_form").fadeIn(1000);
        positionPopup();
    });

    //close popup
    $(".close").click(function () {
        $(".overlay_form").fadeOut(500);
    });
});

//position the popup at the center of the page
function positionPopup() {
    if (!$(".overlay_form").is(':visible')) {
        return;
    }
    $(".overlay_form").css({
        left: ($(window).width() - $('.overlay_form').width()) / 2,
        top: ($(window).width() - $('.overlay_form').width()) / 7,
        position: 'absolute'
    });
}

//maintain the popup at center of the page when browser resized
$(window).bind('resize', positionPopup);