Flutter Searchdelegate，我想在单击搜索时添加背景颜色和应用程序栏颜色

class CustomSearchDelegate extends SearchDelegate {
  @override
  ThemeData appBarTheme(BuildContext context) {
    // 设置应用程序栏颜色
    final ThemeData theme = Theme.of(context);
    return theme.copyWith(
      appBarTheme: theme.appBarTheme.copyWith(
        backgroundColor: Colors.blue, // 设置背景颜色
      ),
    );
  }

  @override
  Widget buildLeading(BuildContext context) {
    // 构建返回按钮
    return IconButton(
      icon: Icon(Icons.arrow_back),
      onPressed: () {
        close(context, null);
      },
    );
  }

  @override
  Widget buildResults(BuildContext context) {
    // 构建搜索结果页面
    return Container();
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    // 构建搜索建议页面
    return Container();
  }
}