Bug with menu bar on mac os el capitan how to fix?

Question

macOS

There is an old macbook about 2012, I noticed a bug when I switch the top menu to a dark theme, such garbage passes https://prnt.sc/fw060d that there is a gap between the program window and the menu, that is, I can’t raise the window above so that it’s perfect adjacent to the menu, I did not find anything similar on the Internet

Answer 1

Dude don't worry it's normal

Answer 2

And how did you do that, what would be black?)))
Come in

Answer 3

This is how it should be
https://yadi.sk/i/SC1DCNkb3L5wQb