How to use same theme for every repo?

I am using and it uses the theme I like, but when I create a new repository and enable GitHub pages, the theme is gone for that repository (which is normal). I want it to use that same theme and act like it’s one website. I could add from my new repo to my website repo, but that is annoying.

Edit: Even if it used the same theme, the websites would be individual from one another. I want the new repo’s website to be a post or blog (*.md) in the main website.