I have finished the Technical Documentation Page, and I would love to hear some feedback. I struggled a lot with the flexbox aspect of it, but in the end I made it work.
There are HTML syntax/coding errors you should be aware of and address.
Since copy/paste from codepen you can ignore the first warning and first two errors.
Codepen provides validators for HTML, CSS and JS. Click on the chevron in the upper right of each section and then click on the respective ‘Analyze’ link.
The one for CSS is good. Use it and address the issue(s). (Be wary of creating mulitple selectors. It can make maintenance hard)
(The one for HTML misses things which is why I recommend W3C)
A suggestion, I see this a lot with this project. This is one where you may want to search for scroll-behavior and see what it can do for you.
It does make for a nice transition from one section to the next when clicking the links.