如何在flutter中使用ShapeBorder类自定义黑色实心圆角边框

dependencies:
  flutter:
    sdk: flutter
  flutter_material:
    sdk: flutter

import 'package:flutter/material.dart';

class CustomShapeBorder extends ShapeBorder {
  @override
  EdgeInsetsGeometry get dimensions => EdgeInsets.all(0);

  @override
  Path getInnerPath(Rect rect, {TextDirection? textDirection}) {
    return Path()..addRect(rect);
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    return Path()
      ..addRRect(RRect.fromRectAndRadius(rect, Radius.circular(10)));
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection}) {
    final paint = Paint()
      ..color = Colors.black
      ..style = PaintingStyle.fill;

    canvas.drawRRect(RRect.fromRectAndRadius(rect, Radius.circular(10)), paint);
  }

  @override
  ShapeBorder scale(double t) {
    return CustomShapeBorder();
  }
}

import 'package:flutter/material.dart';

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 200,
      height: 200,
      decoration: ShapeDecoration(
        shape: CustomShapeBorder(),
      ),
    );
  }
}