Use multiple themes on one website jeykll

I have recently found out about jekyll, and want to make a project landing page with it. I would like to have a home page using one theme (e.g. ubuild) and have another page for the docs (accessed via a navigation bar at the top) that uses a different theme (e.g. just-the-docs). How can I go about doing this?

EDIT: I want to use Github Pages for this.

I solved this with help from @JoostS's answer but with a few modifications:

1. Make an organization on GitHub pages with a repo called <org-name>.github.io. This repo should contain the theme for the home page (ubuild in my case) and all the content for it.

2. Make another repo with a jeykll site, called docs. This site should have the theme you want for the other page (just-the-docs in my case) and all the content along with it.

3. In the docs repo, add baseurl: "/docs" to your _config.yml

4. The <org-name>.github.io repo, should now be hosted at <org-name>.github.io/:

   

5. The docs repo should now be hosted at the <org-name>.github.io/docs url:

   

6. To link to the docs page, you should just be able to use /docs now.