I think that Spain have been a little underestimated in the build up to this competition and I think that Croatia have been slightly overrated. I like Unai Simon is a very good keeper and Spain look good in defence and in the creative area of their team. For me the only player I'm not too crazy about is Morata. He seems to waste a lot of opportunities that come his way, but then again, he has scored some very important goals during his career. But I think Spain look strong and they look like the best team in the group to me.
As for Croatia, no doubt they still have some big names in their team still. But 5 of the 6 players in their midfield and attack are all in their 30's, with Modric now 38 years of age. Croatia's defence is relatively young though, but I still think that dynamic and very talented teams like Spain should get the better of Croatia. 16 year old Lamine Yamal is starting for Spain today against Croatia, which is quite incredible and he will be the youngest player to ever play at a European Championships.
This should be another entertaining match, but I expect Spain to just edge it.