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 {
  border: 1px solid $primary-low;
}

.cooked img.d-lazyload {
  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: $secondary;
  background: $primary;
  opacity: 0;
  transition: opacity 0.2s;
  display: flex;
  align-items: center;

  .filename {
    margin: $meta-element-margin;
    overflow: hidden;
    white-space: nowrap;
    text-overflow: ellipsis;
    // TODO: delete this by May 2019
    &:before {
      // ideally, the SVG used here should be in HTML and reference the SVG sprite
      content: svg-uri(
        '<svg xmlns="http://www.w3.org/2000/svg" width="14px" height="16px" viewBox="0 0 512 512" fill="#{$secondary}"><path d="M464 64H48C21.49 64 0 85.49 0 112v288c0 26.51 21.49 48 48 48h416c26.51 0 48-21.49 48-48V112c0-26.51-21.49-48-48-48zm-6 336H54a6 6 0 0 1-6-6V118a6 6 0 0 1 6-6h404a6 6 0 0 1 6 6v276a6 6 0 0 1-6 6zM128 152c-22.091 0-40 17.909-40 40s17.909 40 40 40 40-17.909 40-40-17.909-40-40-40zM96 352h320v-80l-87.515-87.515c-4.686-4.686-12.284-4.686-16.971 0L192 304l-39.515-39.515c-4.686-4.686-12.284-4.686-16.971 0L96 304v48z"/></svg>'
      );
      margin-right: $meta-element-margin;
      display: inline-block;
      vertical-align: middle;
      opacity: 0.8;
    }
  }

  .d-icon {
    margin: $meta-element-margin;
    opacity: 0.8;
    color: $secondary;
    + .filename {
      margin-left: 0px;
    }
    // TODO: delete this by May 2019
    + .filename:before {
      display: none;
    }
  }

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

  // TODO: delete this by May 2019
  .expand {
    position: absolute;
    bottom: 2px;
    right: 7px;
    &:before {
      // ideally, the SVG used here should be in HTML and reference the SVG sprite
      // the SVG used here is the "expand" icon from FontAwesome 4.7.0
      content: svg-uri(
        '<svg xmlns="http://www.w3.org/2000/svg" width="14px" height="16px" viewBox="0 0 1792 1792" fill="#{$secondary}"><path d="M883 1056q0 13-10 23l-332 332 144 144q19 19 19 45t-19 45-45 19h-448q-26 0-45-19t-19-45v-448q0-26 19-45t45-19 45 19l144 144 332-332q10-10 23-10t23 10l114 114q10 10 10 23zm781-864v448q0 26-19 45t-45 19-45-19l-144-144-332 332q-10 10-23 10t-23-10l-114-114q-10-10-10-23t10-23l332-332-144-144q-19-19-19-45t19-45 45-19h448q26 0 45 19t19 45z"/></svg>'
      );
      opacity: 0.8;
    }
  }
}

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