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

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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Challenge: Build a Technical Documentation Page

Link to the challenge:

Hello, ssebby.

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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