커스텀 위젯으로 하단바 만들어보았는데.. 덮어씌워집니다

숙제에서 나온대로 하단네비게이션바를 커스텀 위젯으로 했는데 
바디 본문이 왜 가려질까요? 

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(),
        body: ListView(
          children: [
            Row(
              children: [
                IconButton(onPressed: (){}, icon: Icon(Icons.person)),
                Text('홍길동'),
              ],
            ),
            Row(
              children: [
                IconButton(onPressed: (){}, icon: Icon(Icons.person)),
                Text('임꺽정'),
              ],
            ),
            Row(
              children: [
                IconButton(onPressed: (){}, icon: Icon(Icons.person)),
                Text('장길산'),
              ],
            ),
          ],
        ),
        bottomNavigationBar: NavBar(),
      )
    );
  }
}

class NavBar extends StatelessWidget {
  const NavBar({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Align(
        alignment: Alignment.bottomCenter,
        child: Container(
            height: 80,
            decoration: BoxDecoration(
                border: Border(
                  top: BorderSide(
                    color: Color.fromRGBO(147, 151, 153, 0.7),
                    width: 1,
                  )
                )
            ),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                IconButton(onPressed: (){}, icon: Icon(Icons.phone), color: Colors.black,),
                IconButton(onPressed: (){}, icon: Icon(Icons.message), color: Colors.black,),
                IconButton(onPressed: (){}, icon: Icon(Icons.contact_page), color: Colors.black,),
              ],
            )
        )
    );
  }
}