code: function forLeft(props: NavigationSceneRendererProps): Object {
    const { position, scene } = props;
    const { index } = scene;
    return {
      opacity: position.interpolate({
        inputRange: [index - 1, index, index + 1],
        outputRange: ([0, 1, 0]: Array<number>),
      }),
    };
  }
docs: Utility that builds the style for the navigation header.
  
  +-------------+-------------+-------------+
  |             |             |             |
  |    Left     |   Title     |   Right     |
  |  Component  |  Component  | Component   |
  |             |             |             |
  +-------------+-------------+-------------+