elevation property
final
The z-coordinate at which to place this bottom app bar relative to its parent.
This controls the size of the shadow below the bottom app bar. The value is non-negative.
If this property is null then BottomAppBarTheme.elevation of ThemeData.bottomAppBarTheme is used. If that's null and ThemeData.useMaterial3 is true, than the default value is 3 else is 8.
Implementation
final double? elevation;