Mobile first design, react router

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

I want to extend this project for my personal use.

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

I wanted to use React Router and this is my first try.

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

I have some issues in Header.jsx with adding event listener to window. Not sure how to fix it.