e.g. to achieve responsive 16:9 images

ratio

  &__image {
    background-color : red;
    position         : relative;
    overflow         : hidden;
    width            : 100%;

    // Top Image (custom ratio image - closer to 4:3 than 16:9)
    &:before {
      display     : block;
      content     : "";
      padding-top : 61.25%;
      width       : 100%;
    }
  }