ajax_default_loader.js

    $(document).ajaxStart(function () {
         $(".loading").show();
    });

    $(document).ajaxComplete(function () {
         $(".loading").hide();
    });

loading_class.css

    .loading {
        display: none;
        position: fixed;
        top: 350px;
        left: 50%;
        margin-top: -96px;
        margin-left: -96px;
        background-color: #ccc;
        opacity: .85;
        border-radius: 25px;
        width: 192px;
        height: 192px;
        z-index: 99999;
    }