curved_btn_nav_main.dart

 @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Bottom Navigation',
      theme: ThemeData(primarySwatch: Colors.green),
      home: Scaffold(
        appBar: AppBar(
          title: Text('Bottom Navigation'),
        ),
        body: _page[_selectedPage],
        bottomNavigationBar: Container(
          decoration: BoxDecoration(
            borderRadius: BorderRadius.only(
                topRight: Radius.circular(30), topLeft: Radius.circular(30)),
            boxShadow: [
              BoxShadow(color: Colors.black12, spreadRadius: 0, blurRadius: 5),
            ],
          ),
          child: ClipRRect(
            borderRadius: BorderRadius.only(
              topLeft: Radius.circular(20.0),
              topRight: Radius.circular(20.0),
            ),
            child: BottomNavigationBar(
              currentIndex: _selectedPage,
              unselectedItemColor: Color.fromRGBO(58, 58, 58, 100),
              selectedItemColor: Colors.green,
              onTap: (int index) {
                setState(() {
                  _selectedPage = index;
                });
              },
              items: [
                //BottomNavigationBarItems... 
              ]
            ),
          ),
        ),
      ),
    );