code: def _calc_font_size(self, win_wd):
          
          font_size = 4
          if win_wd >= 1600:
              font_size = 24
          elif win_wd >= 1000:
              font_size = 18
          elif win_wd >= 800:
              font_size = 16
          elif win_wd >= 600:
              font_size = 14
          elif win_wd >= 500:
              font_size = 12
          elif win_wd >= 400:
              font_size = 11
          elif win_wd >= 300:
              font_size = 10
          elif win_wd >= 250:
              font_size = 8
          elif win_wd >= 200:
              font_size = 6
  
          return font_size
docs: Heuristic to calculate an appropriate font size based on the
          width of the viewer window.
  
          Parameters
          ----------
          win_wd : int
              The width of the viewer window.
  
          Returns
          -------
          font_size : int
              Approximately appropriate font size in points