RaisedButton border code example
Example 1: flutter button border radius
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(18.0),
side: BorderSide(color: Colors.red)
),
Example 2: rounded button flutter
FlatButton(
color: Colors.red,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(18.0)),
child: new Text('round button'),
onPressed: () {},
),