Responsive landing page HTML CSS JavaScript

What are you most proud of, and what would you do differently next time?

I made a triangle with css enjoyed this challenge, I enjoyed this challenge a lot it's trickier than what you might think. Try it you will see.

What challenges did you encounter, and how did you overcome them?

There was a lot challenges in this little challenge had to think real hard some places and play around a lot try to get to this version. Still not completely done but it's close.

What specific areas of your project would you like help with?

I would love it if someone can give some idea's for animating slide out of the navigation menu Slide in is fine slide out have me stuck.