How do you put a border on a raised button?

You can add Border to a raised button by adding a RoundedRecangleBorder as show in below example.

Update

to Change Border Color of ElevatedButton in Flutter ElevatedButton has style Property so we can use the styleFrom method should be used to change the default style of the elevated button. We can change the border color using BorderSide class .

To add a border around a button, we can customize the button’s shape property . The shape requires a RoundedRectangleBorder property. RoundedRectangleBorder further requires a side property and an optional borderRadius property set.