How to remove transparency on stack navigator?

I have created a react native project using react navigation.I have put a picture as a ImageBackground in root component.In android it works fine but in iOS it shows the root component background image but with transparent stack navigators.

    <SafeAreaView style={{ flex: 1 }}>
        <ImageBackground
          source={Assets.bgImage}
          style={{
            width: '100%',
            height: '100%'
          }}
        >
          <Wrapper>{children}</Wrapper>
        </ImageBackground>
      </SafeAreaView>




  {
    initialRouteName: 'SignIn',
    mode: 'card',

    headerMode: 'none',
    transparentCard: true,
    transitionConfig: () => ({
      containerStyle: {
        backgroundColor: 'transparent'
      }
    }),
    /* The header config from HomeScreen is now here */
    defaultNavigationOptions: {
      headerStyle: {
        backgroundColor: 'transparent'
      },
      headerTintColor: '#fff',
      headerTitleStyle: {
        fontWeight: 'bold',
        fontSize: 15
      }
    }
  }

anyone has idea about this issue?