CircleAvatarコンポーネント

  body: Center(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Container(
          width: 200, height: 200,
          child: CircleAvatar(
            backgroundColor: Colors.pink,
            child: Icon(Icons.person, size: 150,),),
        ),
        Container(
          width: 200, height: 200,
          child: CircleAvatar(
            backgroundImage: AssetImage('assets/images/owl.jpg'),
          )
        ),
        Container(
          width: 200, height: 200,
          child: CircleAvatar(
            backgroundColor: Colors.blueAccent,
            child: Text('Flutter', style: TextStyle(fontSize: 50),),
          ),
        ),
      ],
    ),
  ),