Convert px values for multiple property-values pairs to rem values with px fallbacks.

rem Fallback

// ----
// Sass (v3.3.8)
// Compass (v1.0.0.alpha.19)
// ----

$baseFontSize: 16;

@function stripUnit ($num) {
    @return $num / ($num * 0 + 1);
}

@function pxToRem($values) {
  $list: ();
  @each $value in $values {
    @if $value == 0 or $value == auto or unit($value) != px and unitless($value) != true {
      // Ignore 0, auto, and units except px
      $list: append($list, $value);
    }
    @else {
      $remValue: ( stripUnit($value) / stripUnit($baseFontSize) ) * 1rem;
      $list: append($list, $remValue);
    }
  }
  @if length($list) == 1 {
    // return a single value instead of a list,
    // so it can be used in calculations
    @return nth($list, 1);
  }
  @else {
    @return $list;
  }
}

@mixin remFallback($properties) {
  @each $property, $value in $properties {
    @if type-of($value) == list {
      #{$property}: $value;
      #{$property}: pxToRem($value);
    }
    @else if $value == 0 or $value == auto or unit($value) != px and unitless($value) != true {
      // Filter values to avoid errors
      #{$property}: $value;
    }
    @else {
      #{$property}: $value;
      #{$property}: pxToRem($value);
    }
  }
}

.example {
  @include remFallback((
      height: 240 / 2,
      font-size: 13px,
      text-indent: 0,
      left: auto,
      margin: 0 10px 3vh 30%
  ));
}

Libsass doesn't support @each multiple assignments yet, which causes errors on compilation. I discovered a workaround [here](After finding this [issue]%28sass/node-sass#263, I discovered that I can). Adjust the mixin to pass each property:value pair as an item before isolating the $property and $value variables to allow Libsass compile successfully.

@mixin remFallback($properties) {
  @each $val in $properties {
    $property: nth($val, 1);
    $value: nth($val, 2);
    @if type-of($value) == list {
      #{$property}: $value;
      #{$property}: pxToRem($value);
    }
    @else if $value == 0 or $value == auto or unit($value) != px and unitless($value) != true {
      #{$property}: $value;
    }
    @else {
      #{$property}: $value;
      #{$property}: pxToRem($value);
    }
  }
}

Also, had to change the @include statement to reflect this.

.example {
  @include remFallback((
    (height, (240 / 2)),
    (font-size, 13px),
    (text-indent, 0),
    (left, auto),
    (margin, 0 10px 3vh 30%)
  ));
}