I don’t know where is the but style and images of the theme only loads on the home page. But in the /pages/… or /posts/… only the bare HTML of the base of loads is the head and the header but without the CSS and images.
Include a link to the source code repository of your project, because we really need the context of seeing your templates and partials to be able to help you. It is trivial to do a quick git clone on your repo, then run hugo server in your project, to help you out. On the other hand, recreating your code from screenshots, or sort of guessing at it, is not.
If you can’t share your repository for whatever reason, consider creating a dummy repo that you can share, which reproduces the problem you’re experiencing.