scratch.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(body: Test()),
    );
  }
}

class Test extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Material(
      elevation: 3,
      borderRadius: BorderRadius.circular(25),
      color: Colors.black,
      child: TextFormField(
        autocorrect: false,
        validator: (value) =>
        (value?.isEmpty ?? false) ? 'Field is required' : null,
        autovalidateMode: AutovalidateMode.always,
        decoration: InputDecoration(
          filled: true,
          fillColor: Colors.amber,
        ),
      ),
    );
  }
}