@JustSid: I don't know exactly what "delegate based" you means, but the system works like this:
You can create objects, which are stored in structs (the nearest to classes you can get in Lite-C...) with their specific create" function, and you can access their members like engine objects. The objects are "managed" in one loop that calls the respective "manage" function for each object (that's faster than using Caroutines, and I have more control about in which order they are managed).
You can assign them events (like button events) for different things, like when they are destroyed, when windows are maximized, etc. In these functions you can also e.g. prevent a window from being maximized/closed etc.
If "delegate based" means that you write your own function to access the messages of Windows windows and interfere with them, I guess the events can satisfy you. If not, you can change it like you want, because it's open source.

@SchokoKeks: Yes, you can use you own bitmaps and change the sizes of all elements (even at runtime). The bitmaps that you finally see in the demo are made out of smaller ones and built up on runtime (have a look at the "files" folder ).