RaisedButton

Column(
  mainAxisSize: MainAxisSize.min,
  children: <Widget>[
    const RaisedButton(
      onPressed: null,
      child: Text(
        'Disabled Button',
        style: TextStyle(fontSize: 20)
      ),
    ),
    const SizedBox(height: 30),
    RaisedButton(
      onPressed: () {},
      child: const Text(
        'Enabled Button',
        style: TextStyle(fontSize: 20)
      ),
    ),
    const SizedBox(height: 30),
    RaisedButton(
      onPressed: () {},
      textColor: Colors.white,
      padding: const EdgeInsets.all(0.0),
      child: Container(
        decoration: const BoxDecoration(
          gradient: LinearGradient(
            colors: <Color>[
              Color(0xFF0D47A1),
              Color(0xFF1976D2),
              Color(0xFF42A5F5),
            ],
          ),
        ),
        padding: const EdgeInsets.all(10.0),
        child: const Text(
          'Gradient Button',
          style: TextStyle(fontSize: 20)
        ),
      ),
    ),
  ],
)