i want to have borders on the left, right, and top, with a border radius applied to to top left and top right in flutter

I want to have borders with white color on the left, right, and top, with a border radius applied to top left and top right(as the given image) in flutter..! do not want to apply border on bottom(I tried with everything but..)

Do you mean something like this to have all borders except the bottom one of a container?

Here the width for the bottom border is zero and there is no border radius for the bottom corners.

import 'package:flutter/material.dart';

class SomeWidget extends StatelessWidget {
  const SomeWidget({super.key});

  @override
  Widget build(BuildContext context) {
    const BorderSide borderSide = BorderSide(width: 4, color: Colors.white);
    const Radius radius = Radius.circular(20);
    return Center(
      child: Container(
        height: 200,
        width: 200,
        decoration: const BoxDecoration(
          color: Colors.black,
          border: Border(
            left: borderSide,
            right: borderSide,
            top: borderSide,
            bottom: BorderSide(width: 0, color: Colors.white),
          ),
          borderRadius: BorderRadius.only(topLeft: radius, topRight: radius),
        ),
      ),
    );
  }
}

void main() {
  runApp(const MaterialApp(
    home: Scaffold(
      backgroundColor: Colors.green,
      body: SomeWidget(),
    ),
  ));
}