floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
floatingActionButton: Padding(
  padding: const EdgeInsets.all(8.0),
  child: Row(
    mainAxisAlignment: MainAxisAlignment.spaceBetween,
    children: <Widget>[
      FloatingActionButton(
        onPressed: () {},
        child: Icon(Icons.navigate_before),
      ),
      FloatingActionButton(
        onPressed: () {},
        child: Icon(Icons.navigate_next),
      )
    ],
  ),
)