RenderFlex Overflowed when I try to resize screen to smaller one

Question

I am trying to build a page which contains 6 buttons and a background image .My code working perfectly fine . I am creating it for flutter web so I am running it on Edge .When i try resizing the full screen to smaller one i Get the ErroR rENDERED fFlex Overflowed .I tried using expanded widget but i got an error .Can u help me rectify this minor bug. The error is as shown in the image below.

Here is my Code:-

import 'dart:html';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'restaurant.dart';
class mainpage extends StatefulWidget {

  @override
  _mainpageState createState() => _mainpageState();
}

class _mainpageState extends State<mainpage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar:AppBar(
        title:const Center(child: Text("Food express")),
            backgroundColor: Colors.black54,
      ),
      body: Container(
        decoration:const BoxDecoration(
          image:DecorationImage(
              image: AssetImage('image/foood.jpg'),
             fit : BoxFit.cover,
          ),
        ),
           child: Column(
             children: [
               Row(
                 children: [
                   const SizedBox(height:400,width:450),
                   FlatButton(
                     onPressed: () {
                       Navigator.push(context,MaterialPageRoute(builder:(context){
                         return  Restaurant();
                       }));
                     },
                     color: Colors.black26,
                     child: const Text('Restaurant',
                       style: TextStyle(
                         color:Colors.white,
                       ),
                     ),
                     padding: const EdgeInsets.all(40),
                   ),
                   const SizedBox(width:50,height:20),
                   FlatButton(
                     onPressed: () {},
                     color: Colors.black26,
                     child: const Text('Restaurant',
                       style: TextStyle(
                         color:Colors.white,
                       ),
                     ),
                     padding: const EdgeInsets.all(40),
                   ),
                   const SizedBox(width:50,height:20),
                   FlatButton(
                     onPressed: () {},
                     color: Colors.black26,
                     child: const Text('Restaurant',
                       style: TextStyle(
                         color:Colors.white,
                       ),
                     ),
                     padding: const EdgeInsets.all(40),
                   )
                 ],
               ),
              Row(
                children:[
                  const SizedBox(height:100,width:450),
                  FlatButton(
                    onPressed: () {},
                    color: Colors.black26,
                    child: const Text('Restaurant',
                      style: TextStyle(
                        color:Colors.white,
                      ),
                    ),
                    padding: const EdgeInsets.all(40),
                  ),
                  const SizedBox(width:50,height:20),
                  FlatButton(
                    onPressed: () {},
                    color: Colors.black26,
                    child: const Text('Restaurant',
                      style: TextStyle(
                        color:Colors.white,
                      ),
                    ),
                    padding: const EdgeInsets.all(40),
                  ),
                  const SizedBox(width:50,height:20),
                  FlatButton(
                    onPressed: () {},
                    color: Colors.black26,
                    child: const Text('Restaurant',
                      style: TextStyle(
                        color:Colors.white,
                      ),
                    ),
                    padding: const EdgeInsets.all(40),
                  ),
                  const SizedBox(width:50,height:20),
                ]
              )

             ],
           ),


      ),
    );
  }
}