My SCSS rem mixin, with px fallback

sass-rem

@mixin rem($property: font-size, $args: 1rem, $important: false) {
  $em-base: 16px !default;
  $accepted-units: ("px" "rem" "auto" "");
  $rems: ();
  $px: $rems;
  @if $important != false {
    $important: !important;
  } @else {
    $important: '';
  }

  @each $arg in $args {
    $_arg: $arg;
    $unit: '';

    @if $arg == auto {
      $px: join($px, $arg);
      $rems: join($rems, $arg);
    } @else {
      $unit: unit($arg);
      // Unit pre-processing
      @if not index($accepted-units, $unit) {
        @warn "Mixin:rem() : Each value parameter must be one of the following units: #{$accepted-units}.
        Parameters received: #{$args}";
      }
      @if unitless($arg) {
        $_arg: $arg * 1rem;
      } @elseif $unit == "px" {
        $_arg: ($arg / $em-base) * 1rem;
      }

      // Converted parameters collection
      $px: join($px, strip-unit($_arg) * $em-base);
      $rems: join($rems, $_arg);
    }
  }

  // Bam! The output.
  #{$property}: $px unquote($important);
  #{$property}: $rems unquote($important);
}