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SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.5)
// Compass (v1.0.0.alpha.18)
// ----

// @mixin fixed-ratiobox();
// stealed from https://github.com/Team-Sass/toolkit/blob/master/compass/stylesheets/toolkit/_intrinsic-ratio.scss
//
// usage:
// @include fixed-ratiobox(4/3, 50%, 'img, figure');
//
$intrinsic-ratio: 16/9 !default;
$intrinsic-ratio-width: 100% !default;
$intrinsic-ratio-elements: '> *' !default;
$intrinsic-ratio-extend: true !default;
$intrinsic-ratio-direction: top !default;

@mixin intrinsic-ratio-parent($extend: $intrinsic-ratio-extend) {
    @if $extend {
      @extend %intrinsic-ratio-parent;
    }
    @else {
      position: relative;
      height: 0;
    }
}

@mixin intrinsic-ratio-child($extend: $intrinsic-ratio-extend) {
  @if $extend {
    @extend %intrinsic-ratio-child;
  }
  @else {
    display: block;
    position: absolute;
    width: 100% !important; // Nuke the external styles
    height: 100% !important; // Nuke the external styles
    top: 0;
    margin: 0;
    padding: 0;
  }
}

@mixin intrinsic-ratio-ratio($ratio: $intrinsic-ratio, $width: $intrinsic-ratio-width, $direction: $intrinsic-ratio-direction) {
  padding-#{$direction}: (1 / $ratio) * $width;
  width: $width;
}

@mixin intrinsic-ratio($ratio: $intrinsic-ratio, $width: $intrinsic-ratio-width, $elements: $intrinsic-ratio-elements, $extend: $intrinsic-ratio-extend, $direction: $intrinsic-ratio-direction) {
  @include intrinsic-ratio-parent($extend);

  @include intrinsic-ratio-ratio($ratio, $width, $direction);

  @each $element in $elements {
    #{$element} {
            @include intrinsic-ratio-child($extend);
    }
  }
}

@mixin fixed-ratiobox($ratio: $intrinsic-ratio, $width: $intrinsic-ratio-width, $elements: $intrinsic-ratio-elements, $extend: $intrinsic-ratio-extend, $direction: $intrinsic-ratio-direction) {
  @include intrinsic-ratio($ratio, $width, $elements, $extend, $direction);
}

%intrinsic-ratio-parent {
  @include intrinsic-ratio-parent(false);
}

%intrinsic-ratio-child {
  @include intrinsic-ratio-child(false);
}

.some-class {
  @include fixed-ratiobox(16/9, 100%, 'img');
}

SassMeister-output.css

.some-class {
  position: relative;
  height: 0;
}

.some-class img {
  display: block;
  position: absolute;
  width: 100% !important;
  height: 100% !important;
  top: 0;
  margin: 0;
  padding: 0;
}

.some-class {
  padding-top: 56.25%;
  width: 100%;
}