@function strip-unit($number) {
  @if type-of($number) == 'number' and not unitless($number) {
    @return $number / ($number * 0 + 1);
  }

  @return $number;
}

@mixin up($size) {
  $size: strip-unit($size);
  @media (min-width: $size * 1px) {
    @content;

  }
}

@mixin down($size) {
  $size: strip-unit($size);
  @media (max-width: $size * 1px) {
    @content;

  }
}

@mixin between($down, $up) {
  $down: strip-unit($down);
  $up: strip-unit($up);
  @media (min-width: $down * 1px) and (max-width: $up * 1px) {
    @content;

  }
}