Flutter，如何删除对话框周围的空格

我正在从服务器获取数据时调用此对话框.此对话框周围有空格.我可以删除对话框周围的空白.这是我的代码.

var bodyProgress = new Container(
 decoration: new BoxDecoration(
  color: Colors.blue[200],
  borderRadius: new BorderRadius.circular(10.0)
 ),
width: 300.0,
height: 200.0,
//color: Colors.blue,
alignment: AlignmentDirectional.center,
child: new Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
  new Center(
    child: new SizedBox(
      height: 50.0,
      width: 50.0,
      child: new CircularProgressIndicator(
        value: null,
        strokeWidth: 7.0,
      ),
    ),
  ),
  new Container(
    margin: const EdgeInsets.only(top: 25.0),
    child: new Center(
      child: new Text(
        "Signing up...",
        style: new TextStyle(
            color: Colors.white
           ),
         ),
       ),
     ),
   ],
  ),
);

在这里，我正在调用这个对话框.我已经try 使用AlertDialog()和SimpleDialog()，两者都有相同的问题.

showDialog(context: context, child: new AlertDialog(
  content: bodyProgress,

));