@mixin ratio-box ($ratio: 1/1) {

  overflow: hidden;
  position: relative;

  &:before {
    content: "";
    display: block;
    height: 0;
    padding-top: (1 / $ratio) * 100%;
  }

  > img {
      width:100%;
      position:absolute;
      top:0;
      left:0;
  }

}