const BoxShadow({Color color: const Color(0xFF000000), Offset offset: Offset.zero, double blurRadius: 0.0, double spreadRadius: 0.0 })

Creates a box shadow.

By default, the shadow is solid black with zero offset, blurRadius, and spreadRadius.

Source 

const BoxShadow({
  this.color: const Color(0xFF000000),
  this.offset: Offset.zero,
  this.blurRadius: 0.0,
  this.spreadRadius: 0.0
});