How to set top padding for bottom sheet with text field in Flutter?

I need 80 pixel top padding (so AppBar to be shown) for my bottom sheet when keyboard is visible and when keyboard is not visible.

This is my code:

import 'package:flutter/material.dart';

class Temp2Screen extends StatelessWidget {
  const Temp2Screen({super.key});

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: MyWidget(),
      ),
    );
  }
}

class MyWidget extends StatefulWidget {

  MyWidget({Key? key}) : super(key: key);

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

class _MyWidgetState extends State<MyWidget> {

  late ScrollController scrollController;

  List<String> messages = [
    "msg1", "msg2", "msg3", "msg4", "msg5", "msg6", "msg7", "msg8", "msg9", "msg10",
  ];

  @override
  void initState() {
    super.initState();
    scrollController = new ScrollController();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
          child: ElevatedButton(
            onPressed: () {
              showModalBottomSheet(
                  shape: const RoundedRectangleBorder(
                      borderRadius:
                      BorderRadius.vertical(top: Radius.circular(25.0))),
                  backgroundColor: Colors.yellow,
                  context: context,
                  isScrollControlled: true,
                  builder: (context) => Padding(
                    padding: EdgeInsets.only(bottom: MediaQuery.of(context).viewInsets.bottom),
                    child: SizedBox(
                      height: MediaQuery.of(context).size.height - 80,
                      child: Column(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [
                          SingleChildScrollView(
                            child: Column(
                              children: [
                                for (var m in this.messages) ...[
                                  Text(m)
                                ]
                              ],
                            ),
                          ),
                          TextField(
                            textAlign: TextAlign.left,
                            decoration: InputDecoration(
                              hintText: 'Message',
                              contentPadding: EdgeInsets.all(10),
                              border: OutlineInputBorder(
                                borderRadius: BorderRadius.circular(10.0),
                              ),
                              isDense: true,
                            ),
                            keyboardType: TextInputType.multiline,
                            maxLines: 4,
                            minLines: 1,
                            //controller: textController,
                            textInputAction: TextInputAction.send,
                            onSubmitted: (value) {
                              this.setState(() {
                                this.messages.add(value);
                              });
                            },
                          )
                        ],
                      ),
                    ),
                  )
              );
            },
            child: const Text('Show Modal Bottom Sheet'),
          ),
        ));
  }
}

When keyboard is not visible everything is ok (system top panel is visible and AppBar is visible):

However, when keyboard is visible I have a problem as bottom sheet covers both top panel and and AppBar:

Could anyone say how to fix this problem so top panel and AppBar to be visible in both cases (when keyboard is on and when it is off)?