Why? Nothing you have posted so far suggests that your code is using a preprocessor. Why do you think you need to use one?
Paul has already explained this. Any CSS from a local file (one which is not posted online) should be copied into the CSS panel of CodePen.
It has now been explained to you on several occasions how to use CodePen, starting here. If you are still finding it too difficult to use correctly, then I suggest you instead simply post your your code here on the forums. Post the HTML, CSS and JS separately, and use backticks ``` or the </> button in the editor window to format it.