div#ajaxLoadingIndicator {
    display: none;
}

div#ajaxLoadingIndicator.ajaxLoadingOn {
    position: fixed;
    height: 100%;
    width: 100%;
    z-index: 10000;
    background-color: rgba(0, 0, 0, 0.497);
    left: 0px;
    top: 0px;
    background-image: url('Images/loading.gif');
    background-repeat: no-repeat;
    background-position: center center;
    display: block;
}