How to change shadow-root in Java?

Hello.

I downloaded the Bakery App example and I was trying to do some modifications, for example: Instead of having a topbar, create a bar on the left side full vertical.

The problem is: I can’t access on Java class the navbar part, so I can edit the styles to change its width, height and stuff. Anyone with a idea? As I downloaded the Bakery App, I’m trying to do this on the MainView class.

Thanks in advance.