Button decoration

Button

import 'package:flutter/material.dart';

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

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: LoginPage(),
    );
  }
}

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      resizeToAvoidBottomPadding: false,
      body: SingleChildScrollView(
        child: Form(
          child: Container(
            padding: EdgeInsets.only(
                top: 100.0, right: 20.0, left: 20.0, bottom: 20.0),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                SizedBox(height: 200.0),
                buildButtonContainer(),
                SizedBox(
                  height: 30.0,
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }

  Widget buildButtonContainer() {
    return Container(
        height: 56.0,
        width: MediaQuery.of(context).size.width,
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(23.0),
          gradient: LinearGradient(colors: [
            Color(0xFFFF1000),
            Color(0xFF2508FF),
          ], begin: Alignment.centerRight, end: Alignment.centerLeft),
        ),
        child: Center(
          child: Container(
            height: 100.0,
            width: 500.0,
            child: FlatButton(
                shape: new RoundedRectangleBorder(
                    borderRadius: new BorderRadius.circular(20.0)),
                child: Text(
                  "Login",
                  style: TextStyle(
                    color: Colors.white,
                    fontSize: 25,
                  ),
                ),
                onPressed: () {}),
          ),
        ));
  }
}