gray top-level property Null safety

Implementation

NBColor gray = const NBColor(
    0xff71717a,
    <String, Color>{
      'gray.50 ': Color(0xfffafafa),
      'gray.100': Color(0xfff4f4f5),
      'gray.200': Color(0xffe4e4e7),
      'gray.300': Color(0xffd4d4d8),
      'gray.400': Color(0xffa1a1aa),
      'gray.500': Color(0xff71717a),
      'gray.600': Color(0xff52525b),
      'gray.700': Color(0xff3f3f46),
      'gray.800': Color(0xff27272a),
      'gray.900': Color(0xff18181b),
    },
    'gray');