Handle REM values for supporting and non-supporting environments

_rem.scss

$ie: false;
$base: 16px;

@function strip-units($number) {
  @return $number / ($number * 0 + 1);
}

@function convert-to-pixels($value) {
  @if type-of($value) == 'number' {
    $stripped: strip-units($value * $base);
    @return #{floor($stripped)}px;
  } @else {
    $values: unquote('');
    
    @each $px in $value {
      @if $px == 0 {
        $values: append($values, $px);
      } @else {
        $stripped: strip-units($px * $base);
        $values: append($values, #{floor($stripped)}px);
      }
    }
    
    @return $values;
  }
}

@function rem($value) {
  @if $ie {
    @return convert-to-pixels($value);
  } @else {
    @return $value;
  } 
}

.foo {
  width: rem(1.2rem 0);
}

output.css

.foo {
  width: 1.2rem 0;
}