ttk styles

[Peter]

Here is what I came up with - hopefully I have understood the process
correctly and therefore that the comments are correct :-)

I am not sure I have the color of the indicator when it is (de)pressed
correct, but to my eyes the color 'snow' looks like the same color
used with a Tkinter Checkbutton with indicatoron=false.

    r = Tk()

    s = Style()

    # create a layout that excludes the indicator element
    s.layout('NoIndicator.TCheckbutton',
             [('Checkbutton.border',
               {'children': [('Checkbutton.padding',
                              {'children': [('Checkbutton.label',
{})]})]})])

    # Now create(?) a 'setting' for the border appearance of the
checkbutton
    s.theme_settings('default', {
        'NoIndicator.TCheckbutton': {'configure': {'relief': ''}}})

    # set the attributes of the 'setting' to provide the required
behaviour
    s.map('NoIndicator.TCheckbutton',
          relief=[('disabled', 'flat'),
                  ('selected', 'sunken'),
                  ('pressed', 'sunken'),
                  ('active', 'raised'),
                  ('!active', 'raised')],
          background=[('selected', 'snow')])

    button = Checkbutton(r,
                         text='Test',
                         style='NoIndicator.TCheckbutton')
    button.pack()

    r.mainloop()