Template:PosterGalleryCSS.css

/* Card frame for each poster */
.ksi-posters .gallerybox .thumb {
  border: 1px solid #777;
  background: #111;
  padding: 6px;
  box-shadow: 0 1px 4px rgba(0,0,0,.4);
}
.ksi-posters .thumb img { display:block; width:100%; height:auto; }

/* Make caption text WHITE (but do not touch links) */
.ksi-posters .gallerytext {
  color: #fff !important;   /* forces non-link caption text to white */
  font-size: 90%;
  padding-top: 4px;
  text-align: center;
}

/* Ensure any non-anchor elements inside captions inherit the white */
.ksi-posters .gallerytext > :not(a),
.ksi-posters .gallerytext > :not(a) * {
  color: #fff !important;
}

/* ===== Keep links using the site's normal colors ===== */
.mw-parser-output ul.gallery.ksi-posters li.gallerybox .gallerytext a,
.mw-parser-output ul.gallery.ksi-posters li.gallerybox .gallerytext a:visited,
.mw-parser-output ul.gallery.ksi-posters li.gallerybox .gallerytext a:active,
.mw-parser-output ul.gallery.ksi-posters li.gallerybox .gallerytext a:hover,
.mw-parser-output ul.gallery.ksi-posters li.gallerybox .gallerytext a:focus {
  color: revert !important;      /* fall back to skin/site link colors */
  text-decoration: revert;
}