onlyTop method
Redondea solo las esquinas superiores (topLeft + topRight)
Ejemplo:
AppRadiusPartial._().onlyTop(16.0)
// BorderRadius.only(topLeft: Radius.circular(16.0), topRight: Radius.circular(16.0))
Implementation
BorderRadius onlyTop(double radius) => BorderRadius.only(
topLeft: Radius.circular(radius),
topRight: Radius.circular(radius),
);