kouto-swiss/lib/kouto-swiss/mixins/ratio-box.styl

A complete CSS framework for Stylus

ks-ratio-box( ratio = 1/1 )
    ratio = _strip-units( ratio )

    overflow: hidden
    position: relative

    // The container's height, as a percentage of the
    // container's width, is set by assigning
    // padding-top to a pseudo-element.
    &:before
      content: ""
      display: block
      height: 0
      padding-top: (1 / ratio) * 100%

ratio-box = ks-ratio-box unless ks-no-conflict