Some help to extend this plugin

I’m learning to build blocks etc. I’m using your plugin as a base because it’s simple and it’s great (i was using it on one my websites).
The thing is i wondered: did you write the js file, it looks generated by some sort of processor…could you guide me a little on the process you used to create it?

As a learning base i’m trying to extend it to add a background color selector for example.

Not really a support request but if you have a minute to answer that’d be great ?? thanks !