Day tickets are available via the app «TNW Tickets», at the counter of the BVB Customer Service Centre at Barfüsserplatz (Barfi), from the BLT ticket counter at Heuwaage, from kiosks and at the SBB railway station. Day tickets, which have been purchased in advance, must be validated (punched) using the ticket machine before starting your first journey. Day tickets can also be purchased using the ticket machine. The TNW day ticket is only valid in Switzerland.
You can find information about day tickets and the prices, here.
You can find information about crossboarder day tickets (TicketTriRegio, TTRegio), here.