The last step of https://medium.com/flutter/slivers-demystified-6ff68ab0296f

Slivers, Demystified.dart

import 'package:flutter/material.dart';
import 'dart:math' as math;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Collapsing List Demo')),
        body: CollapsingList(),
      ),
    );
  }
}

class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  _SliverAppBarDelegate({
    required this.minHeight,
    required this.maxHeight,
    required this.child,
  });
  final double minHeight;
  final double maxHeight;
  final Widget child;
  @override
  double get minExtent => minHeight;
  @override
  double get maxExtent => math.max(maxHeight, minHeight);
  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return SizedBox.expand(child: child);
  }

  @override
  bool shouldRebuild(_SliverAppBarDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}

class CollapsingList extends StatelessWidget {
  List<Widget> makeHeader(String headerText) {
    final targetKey = GlobalKey();

    return [
      SliverToBoxAdapter(key: targetKey),
      SliverPersistentHeader(
        pinned: true,
        delegate: _SliverAppBarDelegate(
          minHeight: 60.0,
          maxHeight: 200.0,
          child: GestureDetector(
            onTap: () {
              Scrollable.ensureVisible(targetKey.currentContext!,
                  duration: const Duration(milliseconds: 300));
            },
            child: Container(
              color: Colors.lightBlue,
              child: Center(child: Text(headerText)),
            ),
          ),
        ),
      ),
    ];
  }

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: <Widget>[
        ...makeHeader('Header Section 1'),
        SliverGrid.count(
          crossAxisCount: 3,
          children: [
            Container(color: Colors.red, height: 150.0),
            Container(color: Colors.purple, height: 150.0),
            Container(color: Colors.green, height: 150.0),
            Container(color: Colors.orange, height: 150.0),
            Container(color: Colors.yellow, height: 150.0),
            Container(color: Colors.pink, height: 150.0),
            Container(color: Colors.cyan, height: 150.0),
            Container(color: Colors.indigo, height: 150.0),
            Container(color: Colors.blue, height: 150.0),
          ],
        ),
        ...makeHeader('Header Section 2'),
        SliverFixedExtentList(
          itemExtent: 150.0,
          delegate: SliverChildListDelegate(
            [
              Container(color: Colors.red),
              Container(color: Colors.purple),
              Container(color: Colors.green),
              Container(color: Colors.orange),
              Container(color: Colors.yellow),
            ],
          ),
        ),
        ...makeHeader('Header Section 3'),
        SliverGrid(
          gridDelegate: const SliverGridDelegateWithMaxCrossAxisExtent(
            maxCrossAxisExtent: 200.0,
            mainAxisSpacing: 10.0,
            crossAxisSpacing: 10.0,
            childAspectRatio: 4.0,
          ),
          delegate: SliverChildBuilderDelegate(
            (BuildContext context, int index) {
              return Container(
                alignment: Alignment.center,
                color: Colors.teal[100 * (index % 9)],
                child: Text('grid item $index'),
              );
            },
            childCount: 20,
          ),
        ),
        ...makeHeader('Header Section 4'),
        // Yes, this could also be a SliverFixedExtentList. Writing
        // this way just for an example of SliverList construction.
        SliverList(
          delegate: SliverChildListDelegate(
            [
              Container(color: Colors.pink, height: 150.0),
              Container(color: Colors.cyan, height: 150.0),
              Container(color: Colors.indigo, height: 150.0),
              Container(color: Colors.blue, height: 150.0),
            ],
          ),
        ),
      ],
    );
  }
}