Example 1

Shortcode

[gallery ids="..." effect="none" class="custom-style"]

CSS

.custom-style .rgg-img.rgg-in {
  filter: hue-rotate(90deg);
  transition: 1s filter linear, .5s -webkit-filter linear;
}

.custom-style .rgg-img.rgg-in .rgg-caption-container .rgg-caption {
  filter: hue-rotate(-90deg);
  background-color: indianred;
}

Example 2

Shortcode

[gallery ids="..." effect="none" captions_effect="fade" class="custom-style-2"]

CSS

.custom-style-2 .rgg-img .rgg-caption-container .rgg-caption {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100%;
}