Responsive without media queries (HTML | CSS | JS)

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

¯_(ツ)_/¯

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

The background/color seems off, I didn't overcome it Lol. Can't find the right color even with the style-guide. (╯°□°）╯︵ ┻━┻

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

Colors. Probably.

My JavaScript code too, maybe there's an efficient way to do it other than my solution. I'm a little confident with CSS but hey, maybe I'm doing something wrong? The way I use HTML semantics too.

Any opinion helps, thanks~

Here's my advance payment -- (☞ﾟヮﾟ)☞ ❤