Literally translated you can say Snažno Hrvatska, but since in Forza Italia Forza stands more for "Go" then it does for "Strenght" you can translate it like
Naprijed Hrvatska .... or as we in the South say
Naprid Hrvatska
Since we call our boys VATRENI , to most accurate thing to say would be
Naprijed Vatreni
Or you can use this translation from xcen3x