code: function forInitial(props: NavigationSceneRendererProps): Object {
    const { navigationState, scene } = props;
  
    const focused = navigationState.index === scene.index;
    const opacity = focused ? 1 : 0;
    // If not focused, move the scene to the far away.
    const dir = scene.index > navigationState.index ? 1 : -1;
    const translate = focused ? 0 : 1000000 * dir;
    return {
      opacity,
      transform: [{ translateX: translate }, { translateY: translate }],
    };
  }
docs: Utility that builds the style for the card in the cards list.
  
  +-------------+-------------+-------------+
  |             |             |             |
  |             |             |             |
  |             |             |             |
  |    Next     |   Focused   |  Previous   |
  |    Card     |    Card     |    Card     |
  |             |             |             |
  |             |             |             |
  |             |             |             |
  +-------------+-------------+-------------+
   
  Render the initial style when the initial layout isn't measured yet.