How to set border color only for angles

Faced with the further problem: cant set color only for angles and top side problem angles. There is my code of element:

container: {
    backgroundColor: '#0d1117',
    flex: 1,
    marginTop: 30,
    borderTopLeftRadius: 30,
    borderTopRightRadius: 30,
    borderTopWidth: 2,
    borderColor: 'white',
}

If trying to set left and right width then all side changing color. Thought about add another element, but looks like bad idea. Do have somebody any ideas?