class A extends StatelessWidget {
  ScrollController _scrollController = ScrollController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _scrollController.jumpTo(0.0);
        },
      ),
      body: CustomScrollView(
        controller: _scrollController,
        slivers: [
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return Image.network(
                  'https://picsum.photos/seed/${Random().nextInt(99999)}/500/500',
                  height: 200,
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}