dialog coming in moddle of screen flutter code example

Example 1: flutter modal dialog fullscreen

showDialog(        context: context,        builder: (BuildContext context) {          return Dialog(            shape: RoundedRectangleBorder(                borderRadius:                    BorderRadius.circular(20.0)), //this right here            child: Container(              height: 200,              child: Padding(                padding: const EdgeInsets.all(12.0),                child: Column(                  mainAxisAlignment: MainAxisAlignment.center,                  crossAxisAlignment: CrossAxisAlignment.start,                  children: [                    TextField(                      decoration: InputDecoration(                          border: InputBorder.none,                          hintText: 'What do you want to remember?'),                    ),                    SizedBox(                      width: 320.0,                      child: RaisedButton(                        onPressed: () {},                        child: Text(                          "Save",                          style: TextStyle(color: Colors.white),                        ),                        color: const Color(0xFF1BC0C5),                      ),                    )                  ],                ),              ),            ),          );        });

Example 2: flutter modal dialog fullscreen

showGeneralDialog(      context: context,      barrierDismissible: true,      barrierLabel: MaterialLocalizations.of(context)          .modalBarrierDismissLabel,      barrierColor: Colors.black45,      transitionDuration: const Duration(milliseconds: 200),      pageBuilder: (BuildContext buildContext,          Animation animation,          Animation secondaryAnimation) {        return Center(          child: Container(            width: MediaQuery.of(context).size.width - 10,            height: MediaQuery.of(context).size.height -  80,            padding: EdgeInsets.all(20),            color: Colors.white,            child: Column(              children: [                RaisedButton(                  onPressed: () {                    Navigator.of(context).pop();                  },                  child: Text(                    "Save",                    style: TextStyle(color: Colors.white),                  ),                  color: const Color(0xFF1BC0C5),                )              ],            ),          ),        );      });