When I build the Web using FlexibleSpaceBar and check it on the web, not the tool, it is grayed out

I used FlexibleSpaceBar with flutter web. If I run it in Visual Studio code, it works normally. However, when I build it on the web and check it, the widget is grayed out as shown in the picture.

Do you know how to solve it?

enter image description here

Widget test() {
    return Scaffold(
      body: DefaultTabController(
        length: 2,
        child: NestedScrollView(
          headerSliverBuilder: (context, value) {
            return [
              SliverAppBar(
                floating: true,
                pinned: true,
                bottom: TabBar(
                  tabs: [
                    Tab(text: "Posts"),
                    Tab(text: "Likes"),
                  ],
                ),
                expandedHeight: 450,
                flexibleSpace: FlexibleSpaceBar(
                  collapseMode: CollapseMode.pin,
                  background: Container(
                    color: Colors.purple,
                    height: 300,
                  ), // This is where you build the profile part
                ),
              ),
            ];
          },
          body: TabBarView(
            children: [
              Container(
                child: ListView.builder(
                  itemCount: 100,
                  itemBuilder: (context, index) {
                    return Container(
                      height: 40,
                      alignment: Alignment.center,
                      color: Colors.lightBlue[100 * (index % 9)],
                      child: Text('List Item $index'),
                    );
                  },
                ),
              ),
              Container(
                child: ListView.builder(
                  itemCount: 100,
                  itemBuilder: (context, index) {
                    return Container(
                      height: 40,
                      alignment: Alignment.center,
                      color: Colors.lightBlue[100 * (index % 9)],
                      child: Text('List Item $index'),
                    );
                  },
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }