Can someone help me identify why I am unable to link CSS to HTML?
Not without also seeing the CSS and what you see in the browser with the developer tools open. That link looks correct, so there’s probably something else wrong.
I think maybe it’s not linked to the HTML as a sub folder?
css/ folder. Is there a file inside there? If not, that’s your problem. Like I said, though, I can’t say until I see the CSS file that you expect to have been linked.