createStackNavigator
https://stackoverflow.com/questions/51181965/react-navigation-header-has-a-faint-line

<Stack.Navigator
        screenOptions={{
          headerStyle: {
            backgroundColor: currentTheme.themeColor,
            borderBottomWidth: 0,
            elevation: 0,//去掉安卓導航下面白線
            shadowOpacity: 0,//去掉iOS導航下面白線
          },
          headerTintColor: '#fff',
          headerTitleStyle: {
            fontWeight: 'bold',
            alignSelf: "center",
          }, 
        }} 
      >

** createBottomTabNavigator** 去掉tabbar上面的白線
https://stackoverflow.com/questions/60337002/white-line-above-bottomtabnavigator-in-react-native

tabBarOptions={{ 
    style: styles.container
}}

const styles = StyleSheet.create({
  container:{ 
    backgroundColor: currentTheme.themeColor,
    borderTopWidth: 0
  }
})