Sesvete, Croatia, is in area code 01 (or +385 1 in international format), the same as Zagreb.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
The country code and area code of Rijeka, Croatia is 385, (0)51.
The country code and area code of Krapina, Croatia is 385, (0)49.
The country code and area code of Koprivnica, Croatia is 385, (0)48.
The country code and area code of Bjelovar, Croatia is 385, (0)43.
The country code and area code of Cakovec, Croatia is 385, (0)40.
The country code and area code of Gospic, Croatia is 385, (0)53.
The country code and area code of Karlovac, Croatia is 385, (0)47.
The country code and area code of Osijek, Croatia is 385, (0)31.
The country code and area code of Pazin, Croatia is 385, (0)52.
The country code and area code of Sisak, Croatia is 385, (0)44.
The country code and area code of Vinkovci, Croatia is 385, (0)32.
The country code and area code of Virovitica, Croatia is 385, (0)33.