If you are a GameMaker Studio user, this may be one of the most useful extensions available on the internet. It is a a massive improvement to the visual experience, increasing readability 10 fold and makes everything consistent.

It can be improved, but nothing here to be concerned about, the developer clearly knows what he's doing!

Although some pages on the YYG docs site do not load properly, I believe it's more their lack of consistent styling than this addons ability to modify it.