code: def draw_separators(self):
          
          total = 1
          self._timeline.create_line((0, 1, self.pixel_width, 1))
          for index, (category, label) in enumerate(self._category_labels.items()):
              height = label.winfo_reqheight()
              self._rows[category] = (total, total + height)
              total += height
              self._timeline.create_line((0, total, self.pixel_width, total))
          pixel_height = total
          self._timeline.config(height=pixel_height)
docs: Draw the lines separating the categories on the Canvas