showDialog(
  context: context,
  builder: (context) {
    Column(
      children: <Widget>[
        AlertDialog(
          title: Text("タイトル"),
          // コンテンツ領域
          content: SingleChildScrollView(
            child: ListBody(
              children: <Widget>[
                Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: <Widget>[
                    Row(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: <Widget>[
                        FlutterLogo(
                          size: 120.0,
                        ),
                        FlutterLogo(
                          size: 120.0,
                          colors: Colors.yellow,
                        ),
                      ],
                    ),
                    SizedBox(height: 16.0),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: <Widget>[
                        FlutterLogo(
                          size: 120.0,
                          colors: Colors.red,
                        ),
                        FlutterLogo(
                          size: 120.0,
                          colors: Colors.green,
                        ),
                      ],
                    ),
                  ],
                ),
              ],
            ),
          ),
          actions: <Widget>[
            FlatButton(
              child: Text("Cancel"),
              onPressed: () => Navigator.pop(context),
            ),
            FlatButton(
              child: Text("OK"),
              onPressed: () => Navigator.pop(context),
            ),
          ],
          // 角丸
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(20.0),
          ),
        ),
      ],
    );
  }
);