code: def calculate_border_width(self):
          
          return self.max_dimension.width - self.margins.left - self.margins.right - 1
docs: Calculate the width of the menu border. This will be the width of the maximum allowable
          dimensions (usually the screen size), minus the left and right margins and the newline character.
          For example, given a maximum width of 80 characters, with left and right margins both
          set to 1, the border width would be 77 (80 - 1 - 1 - 1 = 77).
  
          Returns:
              int: the menu border width in columns.