how to make curved from the top Flutter bottom navigation bar

I want to make this curved bottom nav bar in Flutter

but what I'm getting is this

I'm using ClipRRect to do it but it's not what I need, and here is my code

      bottomNavigationBar: Container(
        decoration: const BoxDecoration(
          borderRadius: BorderRadius.only(topRight: Radius.circular(500),topLeft: Radius.circular(500),),
          color: Color(0xfff2f2f2),
          boxShadow: [
            BoxShadow(
              color: Colors.grey,
              offset: Offset(5.0, 10.0), //(x,y)
              blurRadius: 20.0,
            ),
          ],
        ),
        child: ClipRRect(
          borderRadius: const BorderRadius.only(topRight: Radius.circular(500),topLeft: Radius.circular(500),),
          child: BottomNavigationBar(
            items: [
              BottomNavigationBarItem(icon: Image.asset(logo,height: HDW().fullHeight(context: context,height: 0.1),color: darkGreen,),label: ''),
              BottomNavigationBarItem(icon: Image.asset(logo,height: HDW().fullHeight(context: context,height: 0.1),color: darkGreen,),label: ''),
            ],
          ),
        ),
      ),

You can use the CustomPaint widget, with it you can build any shape that you want in Flutter

This video can help you to design and implement a custom shape for the bottom navigation bar.

Link: Flutter - Custom Shaped Bottom Navigation Bar