:root {
  --gallery-max-width: 960px; /* match your galleries */
}

.img-lightbox {
  max-width: var(--gallery-max-width);
  margin-inline: auto;
}

.img-lightbox img {
  display: block;
  width: 100%;
  height: auto;
  border-radius: 8px;
}

.img-lightbox figcaption {
  margin-top: 0.4rem;
  color: #666;
  font-size: 0.9rem;
}