通知の赤丸BottomNavigationBarItemに入れる

https://flutteragency.com/how-to-display-notification-badge-on-bottom-navigation-bar-icon/

BottomNavigationBarItemにやる

Stackに

                          Positioned(
                            right: 0,
                            child: Container(
                              padding: const EdgeInsets.all(1),
                              decoration: BoxDecoration(
                                color: Colors.red,
                                borderRadius: BorderRadius.circular(6),
                              ),
                              constraints: const BoxConstraints(
                                minWidth: 12,
                                minHeight: 12,
                              ),
                              child: const Text(
                                '$_counter',
                                style: TextStyle(
                                  color: Colors.white,
                                  fontSize: 8,
                                ),
                                textAlign: TextAlign.center,
                              ),
                            ),
                          ),

だな _counter は数字