#ajax-overlay {
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0, 0, 0, 0.4); /* noir transparent */
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 9999;
  color: #fff;
  font-size: 20px;
}