This code split a flutter app into two parts.

slipt_screen_in_two_parts.dart

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Stack(
      children: <Widget>[
        Positioned(
          top: 0,
          bottom: MediaQuery.of(context).size.height / 2,
          width: double.maxFinite,
          child: Container(
            color: Colors.orangeAccent,
          ),
        ),
        Positioned(
            top: (MediaQuery.of(context).size.height / 2),
            bottom: 0,
            width: double.maxFinite,
            child: Container(
              color: Colors.red,
            ))
      ],
    ) // This trailing comma makes auto-formatting nicer for build methods.
        );
  }

Just a suggestion: Trailing comma everywhere makes formatting nicer. When I started learning Dart, I couldn't understand why the formatting is so ugly until I figured that out.

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Positioned(
            top: 0,
            bottom: MediaQuery.of(context).size.height / 2,
            width: double.maxFinite,
            child: Container(
              color: Colors.orangeAccent,
            ),
          ),
          Positioned(
            top: MediaQuery.of(context).size.height / 2,
            bottom: 0,
            width: double.maxFinite,
            child: Container(
              color: Colors.red,
            ),
          ),
        ],
      ),
    );
  }
}

Thank you