Poner loader, transparente, ocupa toda la pantalla

                                          .ajax-loader  {
    background: transparent url("../images/ajax-loader.gif") no-repeat scroll center;
    position: fixed;
    top: 0;
    left: 0;
    border: 0;
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    background-color: #D0D0D0;
    border-style: none;
    opacity: 0.6;
    filter: alpha(opacity=60);
}