Hello there again Yizuhi,
The Theme should be defined in a separate module and it should be in the Library layer.

(You can check The Architecture Canvas)
For example, the OutSystemsUI itself is a module from this Library layer and that's why you can reuse it across several modules.
Your Theme should have the same logic. Once you create it, since it will be in the Library layer, you may use it in both of your modules (Home module and Core widgets module) :)
And responding to your question, that would create a circular dependency because your Home module would depend on your Core Widgets module (for the blocks) and your Core Widgets module would depend on your Home module (for the Theme). And you should avoid circular dependencies as much as you can!
So, my suggestion: isolate the Theme to another module, consider it as a Library module and you may reuse it for both modules.
Kind regards,
Rui Barradas