MainActivity.java

@Override
public void onConfigurationChanged(Configuration configuration) {
	super.onConfigurationChanged(configuration);

	this.updateDarkMode(configuration);
}

private void updateDarkMode(Configuration configuration) {
    // read the new night mode value
    int currentNightMode = configuration.uiMode & Configuration.UI_MODE_NIGHT_MASK;
    switch (currentNightMode) {
        case Configuration.UI_MODE_NIGHT_NO:
            forceDarkMode(WebSettingsCompat.FORCE_DARK_AUTO);
            setDarkNavigationBar();
            System.out.println("LIGHT THEME");
            break;
        case Configuration.UI_MODE_NIGHT_YES:
            forceDarkMode(WebSettingsCompat.FORCE_DARK_ON);
            setLightNavigationBar();
            System.out.println("DARK THEME");
            break;
    }
}