#include <QtWidgets>

int main(int argc, char** argv)
{
    QApplication app(argc, argv);

    QMainWindow window;

//    window.setStyleSheet("");

    QScrollArea *scrollArea = new QScrollArea(&window);
    QWidget *widget = new QWidget;
    widget->resize(1000, 1000);
    scrollArea->setWidget(widget);
    window.setCentralWidget(scrollArea);

    window.resize(400, 400);
    window.show();

    return app.exec();
}