discourse/app/assets/stylesheets/common/base/lightbox.scss

$meta-element-margin: 6px;

.lightbox-wrapper .lightbox {
  position: relative;
  display: inline-block;
  overflow: hidden;
  &:hover .meta {
    opacity: 0.9;
    transition: opacity 0.5s;
  }
}

.d-lazyload-hidden {
  box-sizing: border-box;
}

.onebox img.d-lazyload-hidden:not(.ytp-thumbnail-image) {
  border: 1px solid var(--primary-low);
}

.cooked img.d-lazyload:not(.animated) {
  transition: opacity 0.4s 0.75s ease;
}

.lightbox-wrapper {
  display: inline-block;
  img {
    object-fit: cover;
    object-position: top;
  }
  &,
  * {
    outline: 0;
  }
}

.meta {
  position: absolute;
  bottom: 0;
  width: 100%;
  color: var(--secondary);
  background: var(--primary);
  opacity: 0;
  transition: opacity 0.2s;
  display: flex;
  align-items: center;

  .filename {
    margin: $meta-element-margin;
    @include ellipsis;
  }

  .d-icon {
    margin: $meta-element-margin;
    opacity: 0.8;
    color: var(--secondary);
    + .filename {
      margin-left: 0px;
    }
  }

  .informations {
    margin: $meta-element-margin;
    padding-right: 20px;
    color: var(--secondary-high);
    font-size: var(--font-0);
    flex-shrink: 0;
    flex-grow: 3;
  }
}

.mfp-preloader .spinner {
  margin: auto;
}

.discourse-no-touch {
  a.lightbox {
    transition: all 0.6s cubic-bezier(0.165, 0.84, 0.44, 1);
  }

  a.lightbox:hover {
    box-shadow: 0 2px 5px 0 rgba(var(--always-black-rgb), 0.2),
      0 2px 10px 0 rgba(var(--always-black-rgb), 0.2);
  }
}