text: import Home from './pages/Home.js';
  import Books from './pages/Books.js';
  import Description from './pages/Description.js';
  
  import { createAppContainer } from 'react-navigation';
  import { createStackNavigator } from 'react-navigation-stack';
  
  const Routes = createAppContainer(
    createStackNavigator({
      Home: {
        screen: Home,
        navigationOptions: {
          header: null
        },
      },
      Books: {
        screen: Books,
        navigationOptions: ({ navigation }) => {
          const title = navigation.state.params.book || 'Books'
          return ({
            title,
          })
        }
      },
      Description: {
        screen: Description,
        navigationOptions: ({ navigation }) => {
          const title = navigation.state.params.item.volumeInfo.title || 'Books'
          return ({
            title,
          })
        }
      },
    },
    { 
      defaultNavigationOptions: {
        headerTintColor: '#ddd',
        headerStyle: {
          backgroundColor: "#6200EE"
        }
      },
      headerLayoutPreset: 'center'
    })
  );
  
  export default Routes;
  