Scaffold(
      body: NestedScrollView(
        headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
          return <Widget>[
            SliverAppBar(
              centerTitle: true,
              expandedHeight: 200.0,
              floating: true,
              elevation: 0,
              pinned: true,
              backgroundColor: Colors.white,
              flexibleSpace: FlexibleSpaceBar(
                centerTitle: true,
                title: DecoratedBox(
                  decoration: BoxDecoration(
                    color: Colors.green,
                    borderRadius: BorderRadius.only(
                      bottomLeft: Radius.circular(20),
                      bottomRight: Radius.circular(20),
                    ),
                  ),
                  child: Container(
                    width: MediaQuery.of(context).size.width,
                    child: Center(child: Text('Hello')),
                  ),
                ),
                background: DecoratedBox(
                  decoration: BoxDecoration(
                    color: Colors.red,
                    borderRadius: BorderRadius.only(
                      bottomLeft: Radius.circular(20),
                      bottomRight: Radius.circular(20),
                    ),
                  ),
                ),
              ),
            ),
          ];
        },
        body: Center(
          child: Text("Sample Text"),
        ),
      ),
    );