AnimatedContainer

bool selected = false;

@override
Widget build(BuildContext context) {
  return GestureDetector(
    onTap: () {
      setState(() {
        selected = !selected;
      });
    },
    child: Center(
      child: AnimatedContainer(
        width: selected ? 200.0 : 100.0,
        height: selected ? 100.0 : 200.0,
        color: selected ? Colors.red : Colors.blue,
        alignment:
            selected ? Alignment.center : AlignmentDirectional.topCenter,
        duration: Duration(seconds: 2),
        curve: Curves.fastOutSlowIn,
        child: FlutterLogo(size: 75),
      ),
    ),
  );
}