Technical Page - can't seem to get step #4 to work regarding the ids

HTML-CSS
1

Hi,
My code is not passing #4 from the list of requirements (the other fails i will deal with them in CSS - of course).
I’ve tried putting the ids in the header but still no good. I have the text of the header in each main-section capitalized in the id plus an underscore for each space.
Do you mind taking a look and giving me a hint, please?
Thanks in advance.

here is a link to the codepen:

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User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.106 Safari/537.36.

Challenge: Build a Technical Documentation Page

Link to the challenge:

2

Hello, ssebby.

You have linked to a blank CodePen. Please edited your post with the correct link.

3

particularly, that is the pen in the freeCodeCamp account, you need to save the pen in your account (using the fork button in the bottom right of the page), then you can save and share your project