How are GUI's really made?

Question

My question is
Gui libraries like Qt and lets say for Windows operating systems how do they create all those graphical user interfaces(windows etc).

Does each

Answer 1

The operating system provides libraries that interface with the monitor/display. In short, GUI libraries such as Qt interact with those libraries of the operating system and creates an easier bridge for you, the programmer to interact with the monitor. For instance, Qt might have a drawLine feature, which underneath is taking care of pixel arrangement related to drawing on the monitor/display for the operating system.