"The sanction has been imposed for the setting-off and throwing of fireworks and missiles, and a pitch invasion by a supporter," European soccer's governing body said in a statement.
Croatian fans celebrated their second goal during the 3-1 victory in Poznan by letting off firecrackers and flares.
A supporter dressed in his country's national team shirt also appeared to come out of the stands and gave Croatia coach Slaven Bilic a kiss on the lips in front of the team bench.
