Add notification observer on Mac

SineStriker

2023-12-27 88b5b56b6a67d93208eae3980af2f30da09dd8ae

 examples/mainwindow/mainwindow.cpp

@@ -299,10 +299,6 @@
        return;
    currentTheme = theme;

#ifdef Q_OS_WIN
    windowAgent->setWindowAttribute(QStringLiteral("dark-mode"), currentTheme == Dark);
#endif

    if (QFile qss(theme == Dark ? QStringLiteral(":/dark-style.qss")
                                : QStringLiteral(":/light-style.qss"));
        qss.open(QIODevice::ReadOnly | QIODevice::Text)) {