main.dart

import 'package:flutter/material.dart';

final 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 StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String selected = 'value1';

  @override
  Widget build(BuildContext context) {
    return DropdownButton<String>(
      dropdownColor: Colors.blue,
      style: TextStyle(color: Colors.white),
      value: selected,
      items: [
        DropdownMenuItem(
          value: 'value1',
          child: Text('value1'),
        ),
        DropdownMenuItem(
          value: 'value2',
          child: Text('value2'),
        ),
        DropdownMenuItem(
          value: 'value3',
          child: Text('value3'),
        ),
      ],
      onChanged: (newValue) {
        setState(() {
          selected = newValue;
        });
      },
    );
  }
}