selectionOverlay property
final
A widget overlaid on the picker to highlight the currently selected entry.
The selectionOverlay widget drawn above the CupertinoPicker's picker wheel. It is vertically centered in the picker and is constrained to have the same height as the center row.
If unspecified, it defaults to a CupertinoPickerDefaultSelectionOverlay which is a gray rounded rectangle overlay in iOS 14 style. This property can be set to null to remove the overlay.
Implementation
final Widget? selectionOverlay;