AnimatedContainer

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(home: MyApp()));

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp>{

  static const Duration _duration = Duration(seconds: 1);

  bool _state = true;
  double _width = 2.0;
  Color _color = Colors.red;

  void _play() => setState((){
    _state=!_state;
    _color= _state?Colors.red:Colors.blue;
    _width = _state?2.0:20.0;
  });

  @override
  Widget build(BuildContext context)=> Scaffold(
    body: GestureDetector(
    onTap:()=> _play(),
    child: Padding(
      padding: EdgeInsets.all(40), 
      child: Stack(
        children: <Widget>[
          Align(
            alignment: Alignment.centerRight,
            child:AnimatedContainer(
              width: 80,
              height: 80,
              duration: _duration,
              color: _color,
          ),),
          Align(
          alignment: Alignment.centerLeft,
          child:AnimatedContainer(
            width: 80,
            height: 80,
            duration: _duration,
            decoration: BoxDecoration(
                color: _color,
                border: Border.all(
                color: Colors.black,
                width: _width,
          ),),),),
        ],
  ),),),);
}