import 'package:flexible_scrollbar/flexible_scrollbar.dart';
import 'package:flutter/material.dart';

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

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final _scrollController = ScrollController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FlexibleScrollbar(
        controller: _scrollController,
        alwaysVisible: true,
        scrollThumbBuilder: (ScrollbarInfo info) {
          return Container(
            width: 50,
            height: info.thumbMainAxisSize,
            decoration: BoxDecoration(color: Colors.black),
          );
        },
        child: ListView(
          controller: _scrollController,
          children: List.generate(
            30,
            (index) {
              return ListTile(title: Text(index.toStringAsFixed(0)));
            },
          ),
        ),
      ),
    );
  }
}