#rewardOverlay {
  position: fixed;
  inset: 0;
  z-index: 9999;
  background: rgba(0, 0, 0, 0.308);

  display: flex;               /* keep layout stable */
  align-items: center;
  justify-content: center;

  opacity: 0;
  visibility: hidden;
  transition: opacity 0.2s ease-out;
}

/* Activated state */
#rewardOverlay.show {
  opacity: 1;
  visibility: visible;
}