def percentage(number)
      unless number.is_a?(Sass::Script::Value::Number) && number.unitless?
        raise ArgumentError.new("$number: #{number.inspect} is not a unitless number")
      end
      number(number.value * 100, '%')
    end
def percentage(number)
      unless number.is_a?(Sass::Script::Value::Number) && number.unitless?
        raise ArgumentError.new("$number: #{number.inspect} is not a unitless number")
      end
      number(number.value * 100, '%')
    end
Converts a unitless number to a percentage.

 @example
   percentage(0.2) => 20%
   percentage(100px / 50px) => 200%
 @overload percentage($number)
   @param $number [Sass::Script::Value::Number]
 @return [Sass::Script::Value::Number]
 @raise [ArgumentError] if `$number` isn't a unitless number