.ajax-progress,
.ajax-progress-overlay {
    position: relative;
}

.ajax-progress .throbber {
    display: block;
    float: none;
    top: 50%;
    right: -40px;
    position: absolute;
}

.ajax-progress-overlay .throbber {
    display: block;
    float: none;
    top: 50%;
    left: 50%;
    position: absolute;
}