flutter floting action button elevation
// The value is always non-negative.
floatingActionButton: FloatingActionButton(
elevation: 6.0, // default elevation
highlightElevation: 12.0, //the elevation when the button is pressed.
hoverElevation: 8.0, // while they have a pointer hovering over them.
focusElevation: 8.0, // while they have focus.
disabledElevation: 0.0, //the elevation when the button is disabled.
onPressed: (){},
child: const Icon(Icons.add),
),