Assessment wanted for HTML task 2 ("Structuring a web page")

Just finished structuring a web page from this task on MDN. Check out my code, please. I have only 1 question: inside the CSS file a “section” selector was written, but I didn’t understand, where should I put the section-tag in HTML code.

Here’s a link: https://codepen.io/Arthur-Arutunyan/pen/VwVOOBG