navigator.js

import { StackNavigator } from 'react-navigation';

// screens are here

const Navigator = StackNavigator({
  Screen1: { screen: Screen1 },
  Screen2: { screen: Screen2 },
  Screen3: { screen: Screen3 },
}, {
  navigationOptions: {
    headerTitle: 'Default App Title',
    headerTitleStyle: {
      color: '#FFF'
    },
    headerStyle: {
      backgroundColor: '#f57c00'
    },
    headerBackTitle: null,
    headerTintColor: '#FFF',
  }
  
// styles   
});