Animated gradient border implementation on card in flutter

.dart

// ignore_for_file: library_private_types_in_public_api

import 'dart:math';

import 'package:flutter/material.dart';


class GradientBorderCard extends StatefulWidget {
  const GradientBorderCard({super.key});

  @override
  _GradientBorderCardState createState() => _GradientBorderCardState();
}

class _GradientBorderCardState extends State<GradientBorderCard> with SingleTickerProviderStateMixin {
  late AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 2),
      vsync: this,
    )..repeat();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: AnimatedBuilder(
        animation: _controller,
        builder: (context, child) {
          return Container(
            width: 300,
            height: 200,
            decoration: BoxDecoration(
              gradient: LinearGradient(
                begin: Alignment.topLeft,
                end: Alignment.bottomRight,
                colors: [
                  Colors.greenAccent,
                  Colors.deepPurpleAccent,
                  Theme.of(context).cardColor,
                  Theme.of(context).cardColor,
                ],
                stops: const [
                  0.0,
                  0.33,
                  0.66,
                  1.0,
                ],
                transform: GradientRotation(_controller.value * 2 * pi),
              ),
              borderRadius: BorderRadius.circular(15),
            ),
            child: Padding(
              padding: const EdgeInsets.all(1),
              child: Card(
                elevation: 4,
                color: Colors.black,
                shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(12),
                ),
                child: const Center(
                  child: Text(
                    '⚡',
                    style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
                  ),
                ),
              ),
            ),
          );
        },
      ),
    );
  }
}