How to align text in a button in flutter?

You should put your ‘Text’ in ‘Align’ to align your text left, right, top, bottom etc. As-

    FlatButton(
                color: Colors.blue,
                textColor: Colors.white,
                padding: EdgeInsets.all(8.0),
                splashColor: Colors.blueAccent,
                onPressed: () {
                  /*...*/
                },
                child: Align(
                  alignment: Alignment.center,
                  child: Text(
                    "Flat",
                    style: TextStyle(fontSize: 20.0),
                    textAlign: TextAlign.center
                  ),
                ))