Widget on a widget with Centering - flutter

Question

I want to put a widget onto other's view.
Here is what I did
In normal version without countdown timer, there is no whitespace inside the screen. It is %50 %50 divided by colours(red and blue).
What I want to do is adding that countdown timer without creating whitespace. Directly adding it onto those colours on the center.
I saw that with Stack it is possible to do. I tried it but couldn't remove the white area.
Here is my code:
#override
Widget build(BuildContext context) {
return Scaffold(
body: new Column(
children: [
Expanded(
flex: 40,
child: new Container(
width: double.infinity,
child: new Column(
children: <Widget>[
box1 = new Expanded(
flex: boxSize1,
child: InkWell(
onTap: () {
clickBox1();
}, // Handle your callback
child: new Container(
alignment: Alignment.topCenter,
color: colorRandom,
),
),
),
TimeCircularCountdown(
unit: CountdownUnit.second,
countdownTotal: 3,
onUpdated: (unit, remainingTime) => print('Updated'),
onFinished: () {
setState(() {
visibility = false;
});
},
),
box2 = new Expanded(
flex: boxSize2,
child: InkWell(
onTap: () {
clickBox2();
}, // Handle your callback
child: new Container(
alignment: Alignment.topCenter,
color: color,
),
),
),
],
),
),
),
],
),
);

Answer 1

#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
children: [
Column(
children: [
Expanded(
child: Container(
color: Colors.blue,
)),
Expanded(
child: Container(
color: Colors.red,
)),
],
),
Center(
child: Container(
height: 200,
width: 200,
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(100),
color: Colors.white,
),
// use your countdown timer widget in child
),
)
],
),
);
}