Generated by SassMeister.com.

SassMeister-input.scss

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

// @mixin x-rem()
//
// mixin for easy use of rem with px as fallback
// usage: @include x-rem(14px);
// usage: @include x-rem(14px, font-size);
// usage: @include x-rem(0 12px 2 1.2, margin);
// usage: @include x-rem(1.5 24px, padding);
//
// thanks to Eric Meyer for https://github.com/ericam/susy
// and Hans Christian Reinl for http://drublic.de/blog/rem-fallback-sass-less/
//
@mixin x-rem($values: $base-fontsize, $property: 'font-size', $base: $base-fontsize) {
  // Create a couple of empty lists as output buffers.
  $px-values: ();
  $rem-values: ();
  // Loop through the $values list
  @each $value in $values {
    // For each property value, if it's in rem or px, derive both rem and
    // px values for it and add those to the end of the appropriate buffer.
    // Ensure all pixel values are rounded to the nearest pixel.
    @if $value == 0 or $value == 0px {
      // 0 -- use it without a unit
      $px-values: join($px-values, 0);
      $rem-values: join($rem-values, 0);
    } @else if type-of($value) == number and not unitless($value) and (unit($value) == px) {
      // px value given - calculate rem value from base-font-size
      $new-rem-value: $value / $base;
      $px-values: join($px-values, round($value));
      $rem-values: join($rem-values, #{$new-rem-value}rem);
    } @else if type-of($value) == number and not unitless($value) and (unit($value) == "%") {
      // % value given - don't add px or rem
      $px-values: join($px-values, #{$value});
      $rem-values: join($rem-values, #{$value});
    } @else if $value == auto {
      // auto - don't add px or rem
      $px-values: join($px-values, auto);
      $rem-values: join($rem-values, auto);
    } @else {
      // unitless value - use those directly as rem and calculate the px-fallback
      $px-values: join($px-values, round($value * $base));
      $rem-values: join($rem-values, #{$value}rem);
    }
  }

  // output the converted rules
  #{$property}: $px-values;
  #{$property}: $rem-values;
}
$base-fontsize: 16px;
.sample {
@include x-rem(14px);
@include x-rem(0 12px 2 1.2, margin);
@include x-rem(1.5 24px, padding);
}

SassMeister-output.css

.sample {
  font-size: 14px;
  font-size: 0.875rem;
  margin: 0 12px 32px 19px;
  margin: 0 0.75rem 2rem 1.2rem;
  padding: 24px 24px;
  padding: 1.5rem 1.5rem;
}