Stuck Embedding CSS Link in HTML Page For SharePoint

I have a custom HTML page that is a single page that takes in WebParts. It is a new WebParts interface and there is no WebPart for adding and hiding HTML.

I have added a in the head section of the HTML and when you load the page the CSS is not loaded. Looking at the code there is no reference to the stylesheet.

Both the CSS and the Site Page are published and the correct version for both appear to be being pulled when you visit their URL.

I have tried adding a new Master Page but that has been nothing but trouble. I just need to adjust some simple CSS for this page.

Any help is greatly appreciated.

Thanks, Josh