Add to excisting GUI project possible?

[IMTRobotPC]

Hi, your stylesheet looks amazing. I am programming a project plus GUI for a scientific project and would like to use it. Is it possible to add the stylesheet to an excisting project? I have tried something but only got unresolved errors.
This is the main function of the project:
`#include "peprobot.h"
#include <QtWidgets/QApplication>
#include "DarkStyle.h"
#include "framelesswindow.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
PEPROBOT w;
w.show();
return a.exec();
}
`
Include paths are set correctly. The .qrc files are added as existing item (not sure if this is the right way)

Many thanks for help. Best regards !