Qt for Python (PySide/Shiboken)

Stylesheets for Widgets are not a complete solution, and there are many broken bits here and there. When wanting to customize applications better, the solution is QtQuick. If you cannot move away from Qt Widgets, you might need to do like many projects (including telegram desktop) where you style the widgets directly and create your own stuff like QFancyPushButton and use that instead, for example: https://github.com/laserpants/qt-material-widgets