Decker is neat. I was in the process of using it the other day, but discovered it did not have much by way of font size adjustment in text fields. You could make a heading, but I didn't see a way to make it bigger or larger than simply being a heading.

Decker fonts are composed of fixed-size bitmaps. The included example "fonts.deck" has a variety of additional fonts to choose from in various sizes, and an editor:

https://beyondloom.com/decker/fonts.html

We also recently gained a library for working with vector-based text:

https://beyondloom.com/decker/hershey.html