Answers for "elevated button border radius"

border radius circle button

.btn {
  height: 300px;
  width: 300px;
  border-radius: 50%;
  border: 1px solid red;
}

rounded ElevatedButton

ElevatedButton(
  onPressed: () {},
  child: Text('Button'),
  style: ElevatedButton.styleFrom(shape: StadiumBorder()),
)
Using RoundedRectangleBorder

ElevatedButton(
  onPressed: () {},
  child: Text('Button'),
  style: ElevatedButton.styleFrom(
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(12), // <-- Radius
    ),
  ),
)
Using CircleBorder

ElevatedButton(
  onPressed: () {},
  child: Text('Button'),
  style: ElevatedButton.styleFrom(
    shape: CircleBorder(),
    padding: EdgeInsets.all(24),
  ),
)
Using BeveledRectangleBorder

ElevatedButton(
  onPressed: () {},
  child: Text('Button'),
  style: ElevatedButton.styleFrom(
    shape: BeveledRectangleBorder(
      borderRadius: BorderRadius.circular(12)
    ),
  ),
)
OutlinedButton
Using StadiumBorder

OutlinedButton(
  onPressed: () {},
  child: Text('Button'),
  style: OutlinedButton.styleFrom(
    shape: StadiumBorder(),
  ),
)
Using RoundedRectangleBorder

OutlinedButton(
  onPressed: () {},
  child: Text('Button'),
  style: OutlinedButton.styleFrom(
    shape: BeveledRectangleBorder(
      borderRadius: BorderRadius.circular(12),
    ),
  ),
)
Using CircleBorder:

OutlinedButton(
  onPressed: () {},
  child: Text('Button'),
  style: OutlinedButton.styleFrom(
    shape: CircleBorder(),
    padding: EdgeInsets.all(24),
  ),
)
Using BeveledRectangleBorder

OutlinedButton(
  onPressed: () {},
  child: Text('Button'),
  style: OutlinedButton.styleFrom(
    shape: BeveledRectangleBorder(
      borderRadius: BorderRadius.circular(12),
    ),
  ),
)