This one shows a label, until you resize the window.  Then the label disappears.  If you shrink the
window back to its original size, the label reappears.
    /usr/local/cpython-3.7/bin/python3 ./just-a-label.py

This one shows an invisible button.  But click the button, and its action is executed.  But you
still cannot see the button.
    /usr/local/cpython-3.7/bin/python3 ./just-a-button.py