My scratch-built graphing webpage

I needed a graph and a popular company quoted me the price of a new BMW, so I made it myself. Absolutely everything is from scratch. I didn't make a single Google search looking for algorithms or for libraries. Please let me know what you guys think. You can try it out at https://demo.canary.earth.

It's nicer on desktop because modern phones don't have finger hover for whatever reason (S4 was the GOAT).