From Bern to Rijeka there is daily bus connection during main summer season, out side of this period there is 3-4 weekly departures. The travel time for the 900 km long bus routes is about 14 hours. In Bern the bus departures from the Car-terminal Neufeld which is situated in the northern part of town by the highway exit Bern-Neufeld, in Rijeka passenger will be dropped off at the main bus station, from where is connecting buses to most parts of Croatia. If you plan to return from Rijeka to Bern, you can see timetable here, as you can see below return tickets are much cheaper then two single tickets.