.loader {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 1000;
    background-color: grey;
    opacity: .8;
}

.ajax-loader {
    position: absolute;
    left: 50%;
    top: 30%;
    margin-left: -32px; /* -1 * image width / 2 */
    margin-top: -32px; /* -1 * image height / 2 */
    display: block;
}