A collection of modern flat themes inspired by Bootstrap. There are more than a dozen built-in themes.
pip install ttkbootstrap
Read for more information about how to use along with full-size screenshots, and other useful information. https://ttkbootstrap.readthedocs.io/en/latest/
Play with a live demo after installing the package
python -m ttkbootstrap
Create your own themes with the built-in TTK Creator. Read the docs for instructions on how to create your own themes.
python -m ttkcreator