Flutter Position Stack 居中

      Padding(
        padding: const EdgeInsets.all(4.0),
        child: Stack(
          children: <Widget>[
            Positioned(
                bottom: 0.0,
                right: 0.0,
                left: 0.0,
                child: Padding(
                  padding: const EdgeInsets.symmetric(horizontal: 8.0),
                  child: Container(
                      color: Colors.blue,
                      child: Center(
                        child: Text('Hello',
                          style: TextStyle(color: Color(0xffF6C37F),
                          fontSize: 46, fontWeight: FontWeight.bold),),
                      )
                  ),
                )
            ),
          ],
        ),
      ),