title: React Native: How do I style NavigationExperimental's NavigationCardStack and NavigationHeader?
body: <p>I am trying to change the background color of <code>NavigationExperimental</code>'s <code>NavigationCardStack</code> by: <code>style={{backgroundColor:'white'}}</code> but it does not work. </p>
  
  <p>Is there a way around it? Or is it not possible? </p>
  
  <p>Also, how can I hide the <code>NavigationHeader</code>'s 1px hairline? I tried doing <code>shadowHidden={true}</code> but it is not provided unfortunately. </p>