thumbShadow property

Shadows cast by the resting thumb, painted outside the glass clip.

When null, uses a soft black shadow at 15% opacity with an 8 logical-pixel blur and a 2 logical-pixel downward offset. An empty list disables it. Each shadow's color alpha is multiplied by the interaction/material fade; its blur, spread and offset remain unchanged while pressing and releasing. This controls the thumb only, independently of glass surface elevation.

To restore the stronger default used before this option was introduced:

thumbShadow: const [
  BoxShadow(
    color: Color.from(alpha: 0.25, red: 0, green: 0, blue: 0),
    blurRadius: 8,
    offset: Offset(0, 2),
  ),
],