It is just curiosity. In Windows, for instance, how Qt interprets the stylesheets? this seems to be trivial, but, how does Qt tells the operating system to change the appearance of the widgets? Which library of methods of the Windows API uses? Does WPF uses the same Windows API libraries?
Cheers,
Qt custom draws all widgets. Qt may, under the hood, call into to OS provided API’s for rendering each widget but a QButton is not an HWND using the BUTTON window class on windows. Qt does seem to use the OS for rendering text on the widgets but only the glyphs, not the complex rendering available in QLabel for example.