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