title: change theme with radio button Qwidget in Qt C++
body: <p>I want to change my application Theme with <code>QRadioButton</code> in the <code>QWidget</code> application.
  can anyone help me?
  I have a Setting class that has some settings and one of them is changing the theme between dark and light.
  it is a C++ app with OpenGL.</p>
  <pre><code>void Settings::on_DarkTheme_clicked()
  {
      
  }
  
  void Settings::on_lightTheme_clicked()
  {
      
  }
  </code></pre>
  <p>what should I have to write in these 2 methods?</p>
  <blockquote>
  <p>I used .qss file like this</p>
  </blockquote>
  <pre><code>int main(int argc, char *argv[])
  {
  
  
  QSurfaceFormat fmt;
  fmt.setVersion(3,3);
  fmt.setProfile(QSurfaceFormat::CoreProfile);
  fmt.setSamples(8);
  fmt.setOption(QSurfaceFormat::StereoBuffers);
  fmt.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
  QSurfaceFormat::setDefaultFormat(fmt);
  
  loadSettings();
  
  App app(argc, argv);
  
  QFile stylesheetFile(&quot;./Combinear.qss&quot;);
  stylesheetFile.open(QFile::ReadOnly);
  QString stylesheet = QLatin1String(stylesheetFile.readAll());
  app.setStyleSheet(stylesheet);
  MainWindow w;
  w.show();
  const auto returnValue = app.exec();
  App::setFinished();
  return returnValue;
  }
  </code></pre>
  <p>but it didn't Work and I'm confused</p>