Can we create and add our own custom themes?

[LutiasKokopelli]

Hello, I just installed this from the Microsoft Store. I am curious about a very specific aspect:

When choosing a different theme from the list of available Pomodoros, it is possible to view the "SourceCode" of that theme, which is how I found this repository.

This made me excited and willing to experiment; but the app does not have a "Create" or "Add" theme button, and since my computer won't tell me where the Microsoft Store installed the app (probably in the forever inaccessible even with administrator access WindowsApps folder), I fear that even if I were to create my own .xaml.cs file, I wouldn't be able to put it in a location where the app could find it.

Is it simply impossible and not intended to be possible to create our own themes at all?