I don't know which documentation you use while studying, but you might bookmark official Oracle documentation. Here's a link to the Maintaining Data Integrity in Application Development chapter of the Oracle Database Application Developer's Guide - Fundamentals book; it says:
Datatypes and Names for Foreign Key Columns
You must use the same datatype for corresponding columns in the dependent and referenced tables. The column names do not need to match.
I apologize if this is not what you are looking for.