Bare minimum coursera dart snippet

import 'package:flutter/material.dart';

void main() {
  var container = Container(
    color: Colors.purple,
    width: 300.0,
    height: 400.0,
    margin: EdgeInsets.all(16.0),
    child: Text("Hello world!"),
  );

  runApp(
    MaterialApp(
      home: Scaffold(
        body: container,
      ),
    ),
  );
}