how to prevent list hiding under tabbar in SliverPersistentHeader in flutter?

Question

I'm making tiktok clone flutter app

now i'm on profile screen

I've making it like this

as you can see ,

when I scroll up , gif list hide under SliverPersistentHeader so pictures are not full size

this is I wanna fix it I wanna prevent hiding under tabbar in SliverPersistentHeader like tiktok profile screen

here's my code

SliverPersistentHeader(
  floating: false,
  pinned: true,
  delegate: _SliverAppBarDelegate(
    TabBar(
      indicatorColor: Constants.kPrimaryOrange,
      labelColor: Colors.black87,
      unselectedLabelColor: Colors.grey,
      tabs: [
        Tab(text: "비디오"),
        Tab(text: "이미지"),
      ],
    ),
  ),
),


body: TabBarView(
  children: [
    /// gif Loading 
    Container( 
    ),
    /// image Loading 
    Container(
    ),
  ],
),


class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  _SliverAppBarDelegate(this._tabBar);

  final TabBar _tabBar;

  @override
  double get minExtent => _tabBar.preferredSize.height;
  @override
  double get maxExtent => _tabBar.preferredSize.height;

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return new Container(
      color: Colors.white,
      child: _tabBar,
    );
  }

  @override
  bool shouldRebuild(_SliverAppBarDelegate oldDelegate) {
    return false;
  }
}