Hi Kaye. Looking at the fixtures on soccer24.com I should have said the games are on 30 May. It is 31 May in my time zone. There are 2 games being played in Zagreb, one in Split, one in Zadar and one in Osijek.
I would talk with the hotel you are staying at before attending a match to get the lie of the land. As I said above, Croatian fans have a less than great reputation. In 2013 UEFA, the body in charge of European football, threatened to kick all of their clubs out of international competitions. This was in response to anti semitic and pro fascist chants and gestures by Croatian fans at games. In Nov 2014 Dinamo Zagreb refused to play a game because one of their spectators was denied entry to a stadium.
Generally the ultra fans tend to sit behind the goals so you would in my opinion be best avoiding these areas.
I love football and have watched it in a number of countries. I am not trying to put you off going. Just want to make sure you get some local advice before heading to the stadium.