How to make child apparition smooth and animated?

readme.md

hopeful-oak-3322

Created with <3 with dartpad.dev.

main.dart

import 'package:flutter/material.dart';

const 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 StatefulWidget {
  
  @override State<MyWidget> createState()=>_MyWidgetState();
  
}

class _MyWidgetState extends State<MyWidget> {
  
  /// Whether to show the additional container?
  bool _showContainer = false;
  
  @override
  Widget build(BuildContext context) {
    return Center(child: 
                  ListView(
                    shrinkWrap:true,
                    children:[
                      Text(
                        'Hello, World!',
                        style: Theme.of(context).textTheme.headlineMedium,
                      ),
                      
                      if(_showContainer)
                      Container(
                        color: Colors.pink, 
                        width: 100, 
                        height: 300,
                        child: const Text("How to make the apparition smooth and animated"),
                      ),
                      
                      
                      ElevatedButton(
                        onPressed: ()=>setState(()=>_showContainer=true),
                        child: const Text("SHOW CONTAINER"),
                      ),
                  ]),
     );
  }
}