Custom theme exposes unformatted Opigno menu

I created a subtheme and upon activating it, my main page instantly exposes the Opigno menu with no formatting. I'm not sure what I'm supposed to do. Here's what the Opigno pages look like now: What do I need to do to properly format the menu?

The sidebar-first is not hidden in custom subtheme

I noticed that what is happening is that the 'sidebar-first' region is visible in the custom theme, but in the default theme, Aristotle, it is missing from the markup, leading me to ask if this could be intentional and managed via code. I'll see if I can find code that would intentionally hide this region. However, I would expect the subtheme to inherit all functionality and styling from, and work exactly like the parent theme until it is overridden, so this seems to be a bug. I've also opened an issue on the project page, located here:

Is there a any guide?

Hello, I have the same issue regarding the Top region, main menu and also the login page. Is there any documents or video guide?