[SCSS] mix_ratio (fixed ratio)

 @mixin mix_ratio($w, $h, $w_m, $h_m) {

  position: relative;

  height: auto;

  &:before {

    content: "";

    display: block;

    @media (max-width: $breakpoint_md - 1) {

      padding-top: percentage($h_m / $w_m);

    }

    @media (min-width: $breakpoint_md) {

      padding-top: percentage($h / $w);

    }

  }

}