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.

>>12
What's sad but true? I'm not clicking that link.