All fonts, colors, bitmaps, and borders used within the data files must be defined as resources. These resources can then be referenced by styles for subsequent use by portals.
In order to make it easy to create data files for a new game system, the Kit includes a large assortment of built-in resources that can be immediately put to use. As such, you can largely ignore the need to define visual resources when developing your data files, allowing you to focus solely on getting the underlying functionality into place first. Once the data files are working the way you want, you can then switch your focus back to the resources and being the process of replacing them with something more suitable to the game system.
The Kit also publishes all of the "system" resources that are used by fundamental HL mechanisms and allows them to be modified. This makes it possible to completely replace the system resources used throughout HL, thereby completely transforming the visual look of the entire HL interface. The Mutants & Masterminds data files provide an excellent example of the extent to which you can transform the HL interface.