Flutter:如何在边界上做平滑的渐变？

import 'package:flutter/material.dart';

Container(
  width: 200,
  height: 200,
  decoration: BoxDecoration(
    border: Border.all(color: Colors.black, width: 2),
  ),
)

Container(
  width: 200,
  height: 200,
  decoration: BoxDecoration(
    border: Border.all(color: Colors.black, width: 2),
    gradient: LinearGradient(
      begin: Alignment.topLeft,
      end: Alignment.bottomRight,
      colors: [Colors.red, Colors.blue],
    ),
  ),
)

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Smooth Gradient'),
        ),
        body: Center(
          child: Container(
            width: 200,
            height: 200,
            decoration: BoxDecoration(
              border: Border.all(color: Colors.black, width: 2),
              gradient: LinearGradient(
                begin: Alignment.topLeft,
                end: Alignment.bottomRight,
                colors: [Colors.red, Colors.blue],
              ),
            ),
          ),
        ),
      ),
    );
  }
}