Html5, Css3, Flexbox, Media.

This is my first project that with JS. I'm happy with the result I've learned a lot with events, with that I made my first Hamburger menu with pseudo-element in Css I studied other selectors, I found the :nth-child() selector very interesting with everything I realize that I should work more on larger projects , because the level of learning is very voluminous. I would like you to see my code and give some tips on how to improve. Thank you very much in advance.