flutter: GestureDetector+transform issue

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  final double dyOffset = -100.0;


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          height: 200.0,
          width: 200.0,
          color: Colors.green.withOpacity(0.3),
          child: Center(
            child: Padding(
              padding: const EdgeInsets.all(8.0),
              child: Transform.translate(
                offset: Offset(0.0, dyOffset),
                child: GestureDetector(
                  onTap: _onTap,
                  child: FlutterLogo(size: 200.0,),
                ),
              ),
            ),
          )
        ),
      )
    );
  }

  void _onTap(){
    print("tap!");
  }
}