On the following link from Croatian Ministry of Foreign and European Affairs:
it is published that starting from 15th July 2021, till 15th August all travellers passing through Slovenia must have either EU digital COVID passport, either one of health certificates about COVID status (negative PCR or antigen test or vaccination certificate, or certificate of recovering from COVID not older than 8 months).
However, the exception is for travellers who will pass through Slovenia within 12 hours.
The nearest place for taking the tests is in Makarska. All information about it is in previous articles published here,.