Looked at so many posts...still can't figure out why GitHub Pages is failing to load CSS when it works locally

I feel like I’m missing something, but if someone could help me out, I would be forever indebted.

Repo: GitHub - nathankkim/nathankkim.github.io

In _config.yml, you have baseurl incorrectly set to a sub-path:

baseurl: "/nathankkim.github.io"

For a whole-domain site, baseurl should be the empty string:

baseurl: ""

I think this is called the user or username domain/site? when the repo name = your username it ends up being the root where all your repos will live. So on this one site there is no baseurl, but on any other repo in this account they will need the baseurl set to your username as they will all be served as sub folders from the username directory.