Signup/registration page is not wrapped in site template


for some themes my signup/registration page is not wrapped in site template. The signup page inhherits the background from somewhere but it never shows a menu and doesn’t inherit the theme style or logo.

Why standard 20-11 or 20-12 is printing the registration page correctly wrapped in site template and why some another themes display it as external page without template and its style?

I would really appreciate any help with this issue.

Is there some function I should use, so my registration page will be displayed correctly?