REM Units w/ Pixel Fallback

remPixelFallback.sass

@mixin rem($property, $values...) {
    $n: length($values);
    $i: 1;

    $pxlist: ();
    $remlist: ();

    @while $i <= $n {
        $itemVal: (nth($values, $i));
        @if $itemVal != "auto"{
            $pxlist: append($pxlist, $itemVal + px);
            $remlist: append($remlist, ($itemVal / 10) + rem);
        }@else{
            $pxlist: append($pxlist, auto);
            $remlist: append($remlist, auto);
        }
        
    
        $i: $i + 1;
    }

    #{$property}: $pxlist;
    #{$property}: $remlist;
}
Usage
.main{
    @inlcude rem("margin", 10, 0);
    @inlcude rem("padding", 10);
    @inlcude rem("font-size", 12);
}