Dart Card宽度与父级匹配

我是新手，所以我想知道如何设置宽度以匹配父布局宽度

new Scaffold(
    body: new Container(
  decoration: new BoxDecoration(color: AppColors.hoBlue),
  child: Padding(
    padding: EdgeInsets.all(20.0),
    child: new Center(
        child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Stack(
          children: <Widget>[
            Row(
              children: <Widget>[
                Expanded(
                  child: Padding(
                    padding: EdgeInsets.all(20.0),
                    child: Card(
                      child: Padding(
                          padding: EdgeInsets.fromLTRB(20, 0.0, 20.0,20.0),
                          child: Column(
                            children: <Widget>[
                               Card(
                                    elevation: 10.0,
                                    child: Padding(
                                      padding: EdgeInsets.all(20.0),
                                      child:
                                      Text("Sign Up Here"),
                                    ),
                                  ),
                              TextField(
                                decoration: InputDecoration(
                                  labelText: "Email",
                                  hintText: "example@mail.com",
                                ),
                                autofocus: true,
                              ),
                              TextField(
                                decoration: InputDecoration(
                                  labelText: "Password",
                                ),
                                autofocus: true,
                              ),
                              SizedBox(
                                width: double.infinity,
                                // height: double.infinity,
                                child: new RaisedButton(
                                  color: AppColors.hoBlue,
                                  child: Text(
                                    "Sign In",
                                    style: TextStyle(
                                      color: Colors.white,
                                      fontFamily: 'Raleway',
                                      fontSize: 22.0,
                                    ),
                                  ),
                                  onPressed: () => print('Sign In'),
                                ),
                              )
                            ],
                          )),
                    ),
                  ),
                ),
              ],
            )
          ],
        ),
      ],
    )),
  ),
));

Result From Code Above个

我需要帮助来制作卡片堆叠和家长喜欢 Result I want个

我已经try 使用堆栈，但是结果卡的父卡覆盖了第一张卡.

我知道一点关于扩展标签的内容，但是在两个方向上都扩展了扩展视图，我不知道怎么做.如果你知道的话帮我，提前谢谢.