@AlexanderB
Hi
If you look here
https://code.woboq.org/qt5/qtbase/src/widgets/styles/qwindowsstyle.cpp.html
in 1894
void QWindowsStyle::drawComplexControl
you can see the use of
QRect groove = proxy()->subControlRect(CC_Slider, slider, SC_SliderGroove, widget);
QRect handle = proxy()->subControlRect(CC_Slider, slider, SC_SliderHandle, widget);
I assume you can get the various parts this way, even you changed it using stylesheet.