soapbox/app/styles/components/media-gallery.scss

.media-gallery {
  box-sizing: border-box;
  margin-top: 8px;
  overflow: hidden;
  border-radius: 4px;
  position: relative;
  width: 100%;
  background-color: var(--brand-color--faint);
}

.media-gallery__item {
  border: 0;
  box-sizing: border-box;
  display: block;
  float: left;
  position: relative;
  border-radius: 4px;
  overflow: hidden;
}

.media-gallery__item-thumbnail {
  cursor: zoom-in;
  display: block;
  text-decoration: none;
  color: var(--primary-text-color--faint);
  line-height: 0;
  position: relative;
  z-index: 1;

  &,
  img,
  canvas {
    height: 100%;
    width: 100%;
  }

  img,
  canvas {
    object-fit: cover;
  }

  &--play-on-hover {
    &::before {
      content: 'GIF';
      position: absolute;
      color: var(--primary-text-color);
      background: var(--foreground-color);
      bottom: 6px;
      left: 6px;
      padding: 2px 6px;
      border-radius: 2px;
      font-size: 11px;
      font-weight: 600;
      pointer-events: none;
      opacity: 0.9;
      transition: opacity 0.1s ease;
      line-height: 18px;
    }

    img {
      position: absolute;
    }

    img,
    &:hover::before {
      visibility: hidden;
    }

    &:hover img {
      visibility: visible;
    }
  }
}

.media-gallery__preview {
  width: 100%;
  height: 100%;
  object-fit: cover;
  position: absolute;
  top: 0;
  left: 0;
  z-index: 0;
  background: var(--background-color);

  &--hidden {
    display: none;
  }
}

.media-gallery__gifv {
  height: 100%;
  overflow: hidden;
  position: relative;
  width: 100%;
}

.media-gallery__item-gifv-thumbnail {
  cursor: zoom-in;
  height: 100%;
  object-fit: cover;
  position: relative;
  width: 100%;
  z-index: 1;
  transform: none;
  top: 0;
}

.media-gallery__item-thumbnail-label {
  clip: rect(1px 1px 1px 1px); /* IE6, IE7 */
  clip: rect(1px, 1px, 1px, 1px);
  overflow: hidden;
  position: absolute;
}

.media-gallery__gifv__label {
  display: block;
  position: absolute;
  color: var(--primary-text-color);
  background: rgba($base-overlay-background, 0.5);
  bottom: 6px;
  left: 6px;
  padding: 2px 6px;
  border-radius: 2px;
  font-size: 11px;
  font-weight: 600;
  z-index: 1;
  pointer-events: none;
  opacity: 0.9;
  transition: opacity 0.1s ease;
  line-height: 18px;
}

.media-gallery__gifv {
  &.autoplay {
    .media-gallery__gifv__label {
      display: none;
    }
  }

  &:hover {
    .media-gallery__gifv__label {
      opacity: 1;
    }
  }
}