BorderRadius.vertical constructor

const BorderRadius.vertical({Radius top: Radius.zero, Radius bottom: Radius.zero })

Creates a vertically symmetric border radius where the top and bottom sides of the rectangle have the same radii.

Implementation 

const BorderRadius.vertical({
  Radius top = Radius.zero,
  Radius bottom = Radius.zero,
}) : this.only(
  topLeft: top,
  topRight: top,
  bottomLeft: bottom,
  bottomRight: bottom,
);