The Crown of Zvonimir is a special hat that used to be worn by kings in a country called Croatia a long time ago. Just like how you have a special hat for dress-up or a costume, this was Croatia's special hat for their king.
Now, this hat was named after a very important person named King Zvonimir. He was a king of Croatia back in the olden days. When he became king, he received a special hat that was decorated with pretty jewels and had a cross on the top. Afterwards, every time a new king was crowned in Croatia, they would wear this special hat too.
But something happened in the past that made this crown so special and important. People believed that whenever they had this crown, their country was safe and protected from enemies. So, over time, the Crown of Zvonimir became a really important symbol for the people of Croatia.
Nowadays, you can't wear this special hat for dress-up or a costume. It is kept in a special museum in Croatia where people can go and see it. People still think of the Crown of Zvonimir as a very important symbol for their country, and it reminds them of their history and traditions.