CodePen does not expect any content outside the body tags.
All meta, link, and script information must be put in the settings section of the HTML editor.
You do not need to/cannot link the CSS in your HTML, if you place the CSS in the appropriate section.
If your project uses React, use the Babel preprocessor, and link the CDN in the appropriate section.
The editors offer the ability to format and analyze your code, providing useful information about forgotten closing tags etc.
In your specific case, you have a few syntax errors, which are indicated in the syntax highlighting:
It appears you might be using the incorrect quotes " as well.
If you are still confused with how to use CodePen, please read the official documentation.