Nice execution. I would have removed the Change font link at the top since it links to the same screen at the bottom. It adds a little bit of confusion. On iOs Chrome it was a little bit too easy to reload the whole page when scrolling inside the options drawer. Perhaps adding a cookie that could remember the last applied settings?
Speaking about the options menu. The icons are a little bit confusing. I think they are clearly separated from each other. How about adding labels?
The tool is also clearly targeted against senior designers who know the typographic language. And that is fine I guess. I would have linked to a help guide in order to explain the differences. That would have made the more inexperienced designers to choose the right set.