spacer_in_custom_scroll_view.dart

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: CustomScrollView( // ↓ここから変更あり
        slivers: [
          SliverFillRemaining(
            hasScrollBody: false,
            child: Column(
              children: [
                const Center(
                  child: Text('Center'),
                ),
                const Spacer(),
                ElevatedButton(
                  onPressed: () {},
                  child: const Text('Example'),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}