learning to customize the filter

So I want to learn how to do this idea that I have as explained in this image:
http://i.imgur.com/PSqoVkK.png
I have the idea in words here:
https://github.com/MayhemYDG/4chan-x/issues/822
And so I suppose I have this to work with:
https://github.com/MayhemYDG/4chan-x
Where should I start, what languages do I have to learn?
I'll have to understand how the code works probably.
Perhaps learn CSS? It's probably not that simple.

you will most likely need to modify
https://github.com/MayhemYDG/4chan-x/blob/v3/src/Filtering/Filter.coffee
to pass the reason for a filter to the code here
https://github.com/MayhemYDG/4chan-x/blob/v3/src/Filtering/PostHiding.coffee#L82
and add your tag elements in where the hidden post is.

read about jabbascript, coffeescript, and the DOM. CSS would only be used to make your tag elements look nice