disabledElevation property Null safety
The z-coordinate at which to place this button when the button is disabled (onPressed is null).
This controls the size of the shadow below the floating action button.
Defaults to the same value as elevation. Setting this to zero makes the floating action button work similar to an ElevatedButton but the titular "floating" effect is lost. The value is always non-negative.
final double? disabledElevation;