Flutter OverlayStylishButtonOnCard.dart

import 'package:flutter/material.dart';

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

/// This Widget is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: MyStatelessWidget(),
      ),
    );
  }
}

/// This is the stateless widget that the main application instantiates.
class MyStatelessWidget extends StatelessWidget {
  MyStatelessWidget({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Stack(
        children: <Widget>[
          
          Card(
            child: Padding(
              padding: EdgeInsets.all(16.0),
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: <Widget>[
                  const ListTile(
                    leading: Icon(Icons.album),
                    title: Text('The Enchanted Nightingale'),
                    subtitle: Text('Music by Julie Gable. Lyrics by Sidney Stein.'),
                  ),
                ],
              ),
            ),
          ),
          
          Positioned(
            bottom: -20,
            
            child: RaisedButton(
              onPressed: () {},
              child: const Text(
                'Get Coupon', 
                style: TextStyle(fontSize: 14)
              ),
            ),
          ),
          
        ],
        alignment: AlignmentDirectional.bottomCenter,
        overflow: Overflow.visible,
      )
    );
  }
}