how to create curved edges in flutter button code example

Example 1: rounded button flutter

FlatButton(
              color: Colors.red,
              shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(18.0)),
              child: new Text('round button'),
              onPressed: () {},
            ),

Example 2: round border button flutter

RawMaterialButton(
  onPressed: () {},
  elevation: 2.0,
  fillColor: Colors.white,
  child: Icon(
    Icons.pause,
    size: 35.0,
  ),
  padding: EdgeInsets.all(15.0),
  shape: CircleBorder(),
)