在屏幕的底部是一个按钮。当按钮被按下时，一个底部的薄片应该在按钮后面向上滑动。
我没能把动画做好。我试着用堆栈。
在下面的抖动代码中，底部的表单没有从屏幕的底部向上滑动，而是从按钮的上方向上滑动。我该如何修复它？

import 'package:flutter/material.dart';

class BottomSheetExample extends StatefulWidget {
  const BottomSheetExample({super.key});

  @override
  State<BottomSheetExample> createState() => _BottomSheetExampleState();
}

class _BottomSheetExampleState extends State<BottomSheetExample> {
  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      backgroundColor: Colors.green,
      bottomSheet: MyBottomSheet(),
      body: Center(child: Text('Body')),
    );
  }
}

class MyBottomSheet extends StatefulWidget {
  const MyBottomSheet({super.key});

  @override
  MyBottomSheetState createState() => MyBottomSheetState();
}

class MyBottomSheetState extends State<MyBottomSheet> {
  double _size = 100;
  bool _large = false;

  void _updateSize() {
    setState(() {
      _large = !_large;
      _size = _large ? 200 : 100;
    });
  }

  @override
  Widget build(BuildContext context) {
    return BottomSheet(
      onClosing: () {},
      builder: (BuildContext context) => Stack(
        children: [
          AnimatedSize(
            curve: Curves.elasticOut,
            duration: const Duration(milliseconds: 2000),
            child: Container(
              color: Colors.amber,
              height: _size,
              padding: const EdgeInsets.all(20),
              child: const Center(child: Text('Bottom Sheet')),
            ),
          ),
          Positioned(
            bottom: 10,
            child: ElevatedButton(
              onPressed: () => _updateSize(),
              child: const Text("Toggle"),
            ),
          ),
        ],
      ),
    );
  }
}