ttkbootstrap comes packaged with a LOT of beautifully styled light and dark themes, which you can view in a demo by typing this command into your terminal after installing ttkbootstrap.
>>> python -m ttkbootstrap
You will see a demo screen that looks like the image below. Change the theme selection in the Select a theme combobox and the demo screen will update to the new theme.
You may also check out the screenshots for the light themes and dark themes.