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
Ah. That would have been good to know! I was looking mostly in the interface for a font size tweaker of some kind.