Pimorize

main.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return
      Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children:
          [
           Row(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: [ NumberButton(i:'7'), NumberButton(i:'8'),NumberButton(i:'9') ]
            ),
           Row(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: [ Text('4'), Text('5'),Text('6') ]
            ),
           Row(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: [ Text('1'), Text('2'),Text('3') ]
            ),
           Row(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: [ Text('0'),Text('.') ]
            ),
          ]
      );
  }
}

class NumberButton extends StatelessWidget {

  const NumberButton({ Key key, this.i = '3',}) : super(key: key);

  
  final String i;
  
  @override
  Widget build(BuildContext context) {
    return Container(
    child: Text(i)
      );
    
  }
}