Flutter: neu

main.dart

// In NeumorphicContainer.build
// ...
return Container(
  decoration: BoxDecoration(
    border: Border(
      top: BorderSide(width: bevel, color: Color(0xFFFFFFFFFF)),
      left: BorderSide(width: bevel, color: Color(0xFFFFFFFFFF)),
      right: BorderSide(width: bevel, color: Color(0xFFFF000000)),
      bottom: BorderSide(width: bevel, color: Color(0xFFFF000000)),
    ),
  ),
  child: Container(
    padding: const EdgeInsets.symmetric(horizontal: 20.0, vertical: 2.0),
    decoration: BoxDecoration(
      border: Border(
        top: BorderSide(width: bevel, color: Color(0xFFFFDFDFDF)),
        left: BorderSide(width: bevel, color: Color(0xFFFFDFDFDF)),
        right: BorderSide(width: bevel, color: Color(0xFFFF7F7F7F)),
        bottom: BorderSide(width: bevel, color: Color(0xFFFF7F7F7F)),
      ),
      color: Color(0xFFBFBFBF),
    ),
    child: child,
  ),
);
// ...