showSettingsDialog function 
 
    
    
    
  Implementation
  void showSettingsDialog(BuildContext context) {
  showGeneralDialog(
    context: context,
    barrierLabel: 'Settings',
    barrierDismissible: true,
    // Darken the background.
    barrierColor: Colors.black54,
    transitionDuration: const Duration(milliseconds: 300),
    pageBuilder: (context, anim1, anim2) {
      return const Align(
        alignment: Alignment.center,
        child: SettingsDialog(),
      );
    },
    transitionBuilder: (context, anim1, anim2, child) {
      return FadeTransition(
        opacity: CurvedAnimation(parent: anim1, curve: Curves.easeOut),
        child: child,
      );
    },
  );
}