utils.java

// Update webview theme
private void forceDarkMode(int mode) {
    // This Dark Mode Strategy sets the css prefers-color-scheme property,
    // instead of trying to automatically convert pages. (Consistent with iOS)
    if (WebViewFeature.isFeatureSupported(WebViewFeature.FORCE_DARK_STRATEGY)) {
        WebSettingsCompat.setForceDarkStrategy(this.bridge.getWebView().getSettings(), WebSettingsCompat.DARK_STRATEGY_WEB_THEME_DARKENING_ONLY);
    }
    if (WebViewFeature.isFeatureSupported(WebViewFeature.FORCE_DARK)) {
        WebSettingsCompat.setForceDark(this.bridge.getWebView().getSettings(), mode);
    }
}

// Update status bar and navigation bar theme
public void setLightNavigationBar(){
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O_MR1) {
        View view = getWindow().getDecorView();

        int flags = view.getSystemUiVisibility();
        flags &= ~View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR;
        view.setSystemUiVisibility(flags);

        Window window = getWindow();
        window.setNavigationBarColor(ContextCompat.getColor(this, R.color.navigationBarColor));
    }
}

public void setDarkNavigationBar() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O_MR1) {
        View view = getWindow().getDecorView();

        int flags = view.getSystemUiVisibility();
        flags |= View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR;
        view.setSystemUiVisibility(flags);

        Window window = getWindow();
        window.setNavigationBarColor(ContextCompat.getColor(this, R.color.navigationBarColor));
    }
}