code: def fmt(self, color):
          
          if utility.is_color(color):
              color = color.lower().strip('#')
              if len(color) in [3, 4]:
                  color = ''.join([c * 2 for c in color])
              return '#%s' % color
          raise ValueError('Cannot format non-color')
docs: Format CSS Hex color code.
          uppercase becomes lowercase, 3 digit codes expand to 6 digit.
          args:
              color (str): color
          raises:
              ValueError
          returns:
              str