[Widget]Container,Column,Rowを使ったパネル画面のサンプル

import 'package:flutter/material.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          appBar: AppBar(
            title: const Text('サンプル'),
            centerTitle: true,
            backgroundColor: Colors.green,
          ),
          body: Container(
            color: Colors.green.shade200,
            padding: const EdgeInsets.all(20.0),
            child: Container(
              decoration: BoxDecoration(
                color: const Color(0x00000000),
                border: Border.all(
                  color: Colors.green,
                  width: 10.0,
                ),
                borderRadius: BorderRadius.circular(32.0),
              ),
              child: Column(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  Padding(
                    padding: const EdgeInsets.only(top: 10.0, right: 10.0),
                    child: Row(
                      mainAxisAlignment: MainAxisAlignment.end,
                      children: const [
                        Icon(Icons.close, size: 60.0),
                      ],
                    ),
                  ),
                  Column(
                    children: const [
                      Text(
                        'Happy',
                        style: TextStyle(fontSize: 60.0),
                      ),
                      Text(
                        'Coding !!',
                        style: TextStyle(fontSize: 60.0),
                      ),
                    ],
                  ),
                  Padding(
                    padding: const EdgeInsets.only(bottom: 20.0),
                    child: Row(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: const [
                        Icon(
                          Icons.pause,
                          size: 60.0,
                        ),
                        SizedBox(
                          width: 20.0,
                        ),
                        Icon(
                          Icons.check,
                          size: 60.0,
                        ),
                        SizedBox(
                          width: 20.0,
                        ),
                        Icon(
                          Icons.stop,
                          size: 60.0,
                        ),
                      ],
                    ),
                  )
                ],
              ),
            ),
          )),
    );
  }
}