>>> from tkinter import ttk
>>> s=ttk.Style()
>>> s.theme_names() """======== if you are under win 8.1 you must see ..
('winnative', 'clam', 'alt', 'default', 'classic', 'vista', 'xpnative') you can use for example 'clam' ===== """
>>> s.theme_use('clam')