To draw with offset is not a problem.
But, unlike MS-DOS, a shadow looks like complex combination of light/dark pixels. Meanwhile I see a possibility to use solid color only.
Walt Disney was right. Surprise: GetBase.SetShadow works fine in CustomView. Each "object", created by
canvas.DrawRectRounded, canvas.DrawCircle etc. has a shadow (exactly this I wanted). Meanwhile base panel is unchanged.