sliver_fill_remaining_example.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Boxy Demo',
      theme: ThemeData.dark(),
      home: Scaffold(body: const MyHomePage()),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverList(
          delegate: SliverChildListDelegate([
            Container(
              color: Colors.red,
              child: Text('a' * 500),
              padding: const EdgeInsets.all(16.0),
            ),
            Container(
              color: Colors.green,
              child: Text('a' * 500),
              padding: const EdgeInsets.all(16.0),
            ),
            Container(
              color: Colors.blue,
              child: Text('a' * 500),
              padding: const EdgeInsets.all(16.0),
            ),
            Container(
              color: Colors.amber,
              child: Text('a' * 500),
              padding: const EdgeInsets.all(16.0),
            ),
          ]),
        ),
        SliverFillRemaining(
          hasScrollBody: false,
          child: Center(
            child: Padding(
              padding: const EdgeInsets.all(8.0),
              child: ElevatedButton(
                child: const Text('A button'),
                onPressed: () {},
              ),
            ),
          ),
        ),
      ],
    );
  }
}