You can also go to family search. There are 2 different records for Croatia, the Delnice Deanery church book where the sight has you input your ancestors information and they give you the matches they have. Also they have the Croatia church books from 1516-1994. If you can't find your ancestors that way this is another way to do it but I warn you its much more difficult.
Google search Family search Croatia when you get to family search go to records do all at beginning then scroll down to the Croatia church records then instead of just putting whatever ancestor you have go to images, if you get to the beginning of the Croatian records there are eight different ways to go forward MILITARY,CIVIL,Catholic is the one with the most towns a huge amount has NOT been index so there are a bunch of records not added just yet. SO IF YOU KNOW what town your ancestor is from you should be set. For best results use a computer instead of a phone, it will be easier.