Morocco's relationship with alcohol is complex, and Casablanca is the city where that complexity is most visible. The big hotels have proper bars; the Ain Diab Corniche has licensed beach clubs and late-night venues; and the city has a genuine bar culture, mostly in the downtown and Corniche areas, that operates with a certain discretion but is not hard to find.
The café culture is entirely different — and more Moroccan. Street-level cafés serving mint tea, coffee, and msemen (flatbreads) are everywhere, and sitting in one for an hour is one of the better ways to watch the city. The cafés around the Marché Central and along Boulevard Mohammed V are the most convivial.
Rick's Café (Old Medina, near Rue Sour Djdid) is the famous one — a recreation of the Bogart film set, now a good restaurant and bar with live piano. La Sqala, in the fortification walls at the edge of the medina, has a beautiful courtyard garden and good Moroccan food alongside drinks. For something more local, the bars along the Corniche at Ain Diab get lively on weekend evenings and stay open late.