title: Flutter add a black outline to top of BottomNavigationBar
body: <p>I am trying to figure out how to add a very subtle black line to the top of a BottomNavigationBar to make it's start more distinct from the rest of the content. AirBnb would be a good example of this.</p>
  
  <p>Is there a way to achieve this with Flutter?</p>
  
  <p>Below is the widget I am currently using to render the BottomNavigationBar and I have attached a sample below where there is a distinct grey line at the top of the navbar for AirBnb.</p>
  
  <pre><code>@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: currentPage,
      bottomNavigationBar: PreferredSize(
        preferredSize: Size.fromHeight(50),
        child: Container (
          decoration: BoxDecoration(
          border: Border.all(color: Colors.black)
          ),
        )
      ),
    );
  }
  </code></pre>
  
  <p>The parent of this Widget:</p>
  
  <pre><code>void main() =&gt; runApp(MaterialApp(
    home: new MyApp(),
    debugShowCheckedModeBanner: true,
  ));
  
  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return Navbar();
    }
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/xwLPp.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/xwLPp.jpg" alt="Sample image from the AirBnb app"></a></p>