Setting --background variable on ioc-content hides my embeded Google Map. How I can change the background and still see my map?
You need to understand how the Google Maps Plugin work: https://github.com/mapsplugin/cordova-plugin-googlemaps/blob/master/README.md#how-does-this-plugin-work-android-ios
It need a transparent Background as the Map is a Native Layer behind the Webview. But you can try this:
import {Environment} from '@ionic-native/google-maps/ngx'
Environment.setBackgroundColor(...);