Не видны кнопки флаттера и некоторые тексты

Question

В этом коде не отображаются две кнопки и текст «Başlamak için»,
, в то время как остальная часть кода работает нормально.

/*
*  giris_widget.dart
*  Deneme4
*
*  Created by kk1.
*  Copyright © 2018 [Company]. All rights reserved.
    */

import 'package:deneme4/values/values.dart';
import 'package:flutter/material.dart';


class GirisWidget extends StatelessWidget {

  void onKlnGirPressed(BuildContext context) {
  }

  void onGrvGirPressed(BuildContext context) {
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      body: Container(
        constraints: BoxConstraints.expand(),
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment(0.5, -0.028),
            end: Alignment(0.5, 0.943),
            stops: [
              0,
              1,
            ],
            colors: [
              Color.fromARGB(255, 80, 0, 255),
              Color.fromARGB(255, 15, 0, 131),
            ],
          ),
        ),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.end,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Align(
              alignment: Alignment.topCenter,
              child: Container(
                width: 144,
                height: 90,
                margin: EdgeInsets.only(bottom: 162),
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  children: [
                    Text(
                      "Kerem",
                      textAlign: TextAlign.left,
                      style: TextStyle(
                        color: AppColors.primaryBackground,
                        fontFamily: "Lucida Grande",
                        fontWeight: FontWeight.w400,
                        fontSize: 46,
                      ),
                    ),
                    Spacer(),
                    Align(
                      alignment: Alignment.topRight,
                      child: Container(
                        margin: EdgeInsets.only(right: 47, bottom: 4),
                        child: Text(
                          "APP",
                          textAlign: TextAlign.left,
                          style: TextStyle(
                            color: AppColors.primaryBackground,
                            fontFamily: "",
                            fontWeight: FontWeight.w400,
                            fontSize: 20,
                          ),
                        ),
                      ),
                    ),
                  ],
                ),
              ),
            ),
            Container(
              height: 286,
              margin: EdgeInsets.only(left: 14, right: 13),
              child: Stack(
                alignment: Alignment.center,
                children: [
                  Positioned(
                    left: 0,
                    right: -0,
                    child: Container(
                      height: 286,
                      decoration: BoxDecoration(
                        borderRadius: BorderRadius.all(Radius.circular(15)),
                      ),
                      child: Image.asset(
                        "assets/images/c1.png",
                        fit: BoxFit.cover,
                      ),
                    ),
                  ),
                  Positioned(
                    top: 27,
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.stretch,
                      children: [
                        Align(
                          alignment: Alignment.topCenter,
                          child: Text(
                            "Başlamak için\n",
                            textAlign: TextAlign.left,
                            style: TextStyle(
                              color: AppColors.primaryText,
                              fontFamily: "Lucida Grande",
                              fontWeight: FontWeight.w400,
                              fontSize: 17,
                            ),
                          ),
                        ),
                        Align(
                          alignment: Alignment.topCenter,
                          child: Container(
                            width: 285,
                            height: 48,
                            margin: EdgeInsets.only(top: 11),
                            child: FlatButton(
                              onPressed: () => this.onKlnGirPressed(context),
                              color: Color.fromARGB(255, 21, 200, 114),
                              shape: RoundedRectangleBorder(
                                borderRadius: BorderRadius.all(Radius.circular(24)),
                              ),
                              textColor: Color.fromARGB(255, 0, 0, 0),
                              padding: EdgeInsets.all(0),
                              child: Text(
                                "KULLANICI GİRİŞİ",
                                textAlign: TextAlign.left,
                                style: TextStyle(
                                  color: AppColors.primaryText,
                                  fontFamily: "Lucida Grande",
                                  fontWeight: FontWeight.w400,
                                  fontSize: 15,
                                ),
                              ),
                            ),
                          ),
                        ),
                        Align(
                          alignment: Alignment.topCenter,
                          child: Container(
                            width: 285,
                            height: 48,
                            margin: EdgeInsets.only(top: 16),
                            child: FlatButton(
                              onPressed: () => this.onGrvGirPressed(context),
                              color: AppColors.secondaryElement,
                              shape: RoundedRectangleBorder(
                                borderRadius: BorderRadius.all(Radius.circular(24)),
                              ),
                              textColor: Color.fromARGB(255, 0, 0, 0),
                              padding: EdgeInsets.all(0),
                              child: Text(
                                "GÖREVLİ GİRİŞİ",
                                textAlign: TextAlign.left,
                                style: TextStyle(
                                  color: AppColors.primaryText,
                                  fontFamily: "Lucida Grande",
                                  fontWeight: FontWeight.w400,
                                  fontSize: 15,
                                ),
                              ),
                            ),
                          ),
                        ),
                      ],
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}