cyan top-level property Null safety

Implementation

NBColor cyan = const NBColor(
    0xff06b6d4,
    <String, Color>{
      'cyan.50 ': Color(0xffecfeff),
      'cyan.100': Color(0xffcffafe),
      'cyan.200': Color(0xffa5f3fc),
      'cyan.300': Color(0xff67e8f9),
      'cyan.400': Color(0xff22d3ee),
      'cyan.500': Color(0xff06b6d4),
      'cyan.600': Color(0xff0891b2),
      'cyan.700': Color(0xff0e7490),
      'cyan.800': Color(0xff155e75),
      'cyan.900': Color(0xff164e63),
    },
    'cyan');