exhibition_ bottom_sheet.dart

class _ExhibitionBottomSheetState extends State<ExhibitionBottomSheet>
    with SingleTickerProviderStateMixin {
  ...
  @override
  Widget build(BuildContext context) {
    return ...
            child: Container(
              padding: const EdgeInsets.symmetric(horizontal: 32),
              decoration: const BoxDecoration(
                color: Color(0xFF162A49),
                borderRadius: BorderRadius.vertical(top: Radius.circular(32)),
              ),
              child: Stack(           //<-- Add a stack
                children: <Widget>[
                  MenuButton(),       //<-- With a menu button
                ],
              ),
            ),
     ...
  }
}

class MenuButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Positioned(      //<-- Align the icon to bottom right corner
      right: 0,
      bottom: 24,
      child: Icon(
        Icons.menu,
        color: Colors.white,
        size: 28,
      ),
    );
  }
}