Change Container to AnimatedContainer

Now simply change the Container Widget to AnimatedContainer Widget and provide your desired duration to it. 

And Just by simply adding this you got yourself a cooler UX for your app or website :)

AnimatedContainer(
            duration : const Duration(seconds : 1),
            width: bigger ? 600 : 450,
            height: bigger ? 400 : 300,
            color: Colors.orange,
            child: ...
)