$em-base: if(variable-exists(default-font-size), $default-font-size, 16px);

@function rem($pxval) {
  @if not unitless($pxval) {
    $pxval: strip-units($pxval);
  }

  $base: $em-base;
  @if not unitless($base) {
    $base: strip-units($base);
  }
  @return ($pxval / $base) * 1rem;
}

@function em($pxval, $base: $em-base) {
  @if not unitless($pxval) {
    $pxval: strip-units($pxval);
  }
  @if not unitless($base) {
    $base: strip-units($base);
  }
  @return ($pxval / $base) * 1em;
}

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