flutter change android default font size

/// Android has different 'textscalefactor' settings, like:
  /// 'Small: 0.85', 'Default: 1.0', 'Large: 1.15', 'Largest: 1.3'
/// To make sure the text in your app stays as you intended it to,
  /// use the MediaQuery Widget to overwrite the system default:
@override
  Widget build(BuildContext context) {
    return MediaQuery(
      data: MediaQuery.of(context).copyWith(textScaleFactor: 1.15), // Large
      child: Scaffold(),
    ),
  };      

MaterialApp(
  title: 'Custom Fonts',
  // Set Raleway as the default app font.
  theme: ThemeData(fontFamily: 'Raleway'),
  home: MyHomePage(),
);