Temperature Converter in Vanilla JavaScript

As far as simple projects go, this one is right up there with the nest of them. I took the idea of a temperature converter and applied some visual interest. At it's core, the project is made up of two basic functions -- one to convert the temperature in each direction and the other to change the color of each temperatures' background. I wrote this project several months ago, when I was just diving into front end using vanilla javascript. I'm sure that if I were to refactor this code today, it would look much cleaner.

If you'd like to play with the actual project, check it out here.