Why there is a difference in BottomAppBar height on android and ios with flutter?

I have implemented a bottom app bar in a flutter app, but the height in both the devices are different and even the margin also.

main.dart

bottomNavigationBar: BottomAppBar(
    color: Colors.black,
    child: IconButton(
      onPressed: () {},
    icon: Icon(
        Icons.fiber_manual_record,
        color: Colors.white,
      ),
    ),
  ),