Error with styles in backoffice

[Donio3d]

Hey everyone. I recently gave theme support access to backoffice, but all they did is nothing and messing up my backoffice.

I'm using Prestashop 1.7.6.0 (and for some reasons I can't switch to newer version, so update is not an option). Everything was fine, but now I discovered that some backoffice pages (products, brands, attributes) are totally messed up.

I thought it's about backoffice styles, so I reuploaded working ones from backup /prestashop_catalog/admin/themes > both new-theme and default with styles, but it didn't worked. The key is that my backup have some weeks and I would prefer to keep my changes if restoring is not the only way.

I found out that it lacks styles from classes, for example notification-center:

And it's why I tried with admin/themes. The problem occurs only on some pages, not all.

Any other ideas how to fix that or find problem?

Thanks in advance :)

 

[Donio3d]

Maybe that'll also help (bottom one is my backup running on localhost), as example avatar styles:

[Donio3d]

I found out that it's problem with bootstrap. Anyway I can't manage to put it back to work. Any ideas?