Transparent navigation bar

Hi guys, I need to make something like fake home screen. I made a background with few icons for now, which looks pretty real I think, but navigation bar has a black background. I have to make it transparent. As far as I know, I could do it with few lines of codes in themes.xml and styles.xml. My question is. Where to put that xml files? Which folder in Unity?

This is which nav bar I have and which I need.

I've tried to change themes in AndroidManifest.xml (Assets/Plugins/Android) but I didnt notice any change. Doesn't matter which theme I used navigation bar is always black with few dots on it.

Any ideas? Thank you.