Check out example codes for "circular indicator gets whole page flutter". It will help you in understanding the concepts better.

Code Example 1

@override
    Widget build(BuildContext context) {
      return Container(
        child: Center(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: <Widget>[
              SizedBox(
                child: CircularProgressIndicator(),
                height: 200.0,
                width: 200.0,
              ),
              SizedBox(
                child: CircularProgressIndicator(),
                height: 50.0,
                width: 50.0,
              ),
              SizedBox(
                child: CircularProgressIndicator(),
                height: 10.0,
                width: 10.0,
              )
            ],
          ),
        ),
      );

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