title: Fully transparent CupertinoNavigationBar possible?
body: <p>I am using a <code>CupertinoTabScaffold</code> with a couple of <code>CupertinoTabView</code>s and <code>CupertinoPageScaffold</code>s.</p>
  
  <p>This is my setup:</p>
  
  <pre><code>CupertinoPageScaffold(
     navigationBar: CupertinoNavigationBar(
       backgroundColor: Colors.transparent,
     ),
     child: ...
  )
  </code></pre>
  
  <p>The problem is that I want a large header image which extends behind the navigation bar. According to the Flutter docs the background gets a blurry effect once the backgroundColor has some transparency.</p>
  
  <p>So I cannot find a way to make this navigation bar completely transparent.</p>
  
  <p>Any ideas?</p>
  
  <p>Thanks!</p>