如何在Dart中增加字体大小

我是Flutter + Dart的新手，正在尝试增加字体大小，但很难理解文档并实现我的工作。这是文件。我该如何解决我的问题？

import 'package:flutter/material.dart';

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



class NewApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text('App Header'),
        ),
        body:  new Column(
          children: [
            new Container(
              margin: new EdgeInsets.all(10.0),
              child: new Card(
                child: new Column(
                  children: <Widget>[
                    new Container(
                      padding: new EdgeInsets.all(10.0),
                      child: new Text('Hello Macaw'),
                    ),
                  ],
                ),
              ),
            )
          ],
        ),
      ),
    );
  }
}