cannot change QStatusBar background color

[cic]

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QMainWindow window;
    QStatusBar statusBar;
    QPalette palette;
 
    window.setWindowTitle("QMainWindow with Colored QStatusBar");
    window.setFixedSize(300,100);
    window.setStatusBar(&statusBar);
 
    palette.setColor(QPalette::Background, Qt::red);
 
    statusBar.setPalette(palette);
    statusBar.showMessage("Red QStatusBar");
    window.show();
 
    return app.exec();
}

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

    QMainWindow window;
    QStatusBar statusBar;
    QPalette palette;

    window.setWindowTitle("QMainWindow with Colored QStatusBar");
    window.setFixedSize(300,100);
    window.setStatusBar(&statusBar);

    palette.setColor(QPalette::Background, Qt::red);

    statusBar.setPalette(palette);
    statusBar.showMessage("Red QStatusBar");
    window.show();
    
    return app.exec();
}

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i used the example code but the background color remained as the default one.
any idea?

4.jpg