Need large buttons, minimize, close etc for box standard QMessageBox, for touch screen
I need large buttons , because it is difficult to touch any small area with a large finger. I don't want to rewrite all the widgets already created and available in Qt. How can I change the size of buttons, the minimize close etc, for example a QMessageBox?
Anything that is on the window frame is out of Qt hands. It's the window manager that is responsible for these controls.
There might be an OS specific solution but it's not a Qt topic. Usually it comes down to discarding the window manager frame entirely and drawing it yourself as part of the client area.
As for what's inside the client frame, Qt respects most systems settings, eg. on Windows it will respect your DPI settings. If you want to override some of these you can use for example "qss":http://qt-project.org/doc/qt-5/stylesheet-reference.html to set margins, paddings and font sizes on specific or all widgets.