main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: HomePage());
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Layout Demo')),
      body: CustomScrollView(
        slivers: <Widget>[
          SliverList.list(
            children: [Text('Item 1'), Text('Item 2'), Text('Item 3')],
          ),
          SliverFillRemaining(
            hasScrollBody: false,
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                Spacer(),
                Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: FilledButton(
                    child: Text('Bottom'),
                    onPressed: () {},
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}