FlatButton

FlatButton(
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.only(
      topRight: Radius.circular(20),
    ),
  ),
  color: kPrimaryColor,
  onPressed: () {},
  child: Text(
    "Buy Now",
    style: TextStyle(
      color: Colors.white,
      fontSize: 16,
    ),
  ),
)