https://docs.python.org/3/library/tk.html
https://realpython.com/python-gui-tkinter/#adding-a-widget
- 19_tk_pomodoro_menu_class.py
- 20_tk_number_generator.py
https://docs.python.org/3/library/tk.html
https://realpython.com/python-gui-tkinter/#adding-a-widget