A321 Pilot reported the loss of electrical power resulting in a dark cockpit at the top of climb. The flight crew diverted to make a precautionary landing.

Narrative

Normal departure from ZZZ1-ZZZ2. At TOC reaching 330000 ft.; the cockpit went dark; including CRTs. ISIS remained. CRTs came back on quickly; but rest of cockpit remained dark (no backlighting). Autopilot disengaged; a series of warning messages began to present on Electronic Centralized Aircraft Monitor (ECAM); with associated aural warnings. The Captain took control of the aircraft and turned towards the lights of ZZZ3. The First Officer retrieved his flashlight and began to complete Quick Reference Checklist (QRC) actions. We [requested priority handling] and stated intentions to divert to ZZZ3. After ECAM actions complete; Transferred controls to First Officer. QRH procedures included starting the APU; and were completed approximately 20 minutes after event. This restored cockpit lighting; Blue Hydraulic system and autopilot. A landing assessment was completed; the controls were transferred to the Captain; and we landed in ZZZ3 approximately 15000 lbs overweight. We were met by Crash Fire Rescue (CFR); taxied off the runway onto a taxiway and waited for the brake temperatures to stabilize. The Brake temperatures reached a maximum of 365 degrees C. before beginning to cool. We then taxied to the gate under our own power.The sudden loss of lighting while flying at night added seconds to reaction time to recognize and assess presentation of failures. We were faced with a cascade of failures including GEN 1 fault; AC BUS FAULT; TR 1; BLUE hydraulic; auto flight; auto thrust; brakes; F/CTRL; ENG mode; GEN 1 fault; etc. The Exact problem was challenging to assess due to the number of warnings and messages occurring simultaneously. The loss of lighting compounded the difficulties. It was unclear what; if anything; was working (such as COMMS) as we were using flashlights to set the FCU; com radios; etc. We followed the procedures of the QRC/ECAM actions methodically. Some ECAM actions caused associated messages and it became difficult to sort out the associated messages from the system failures. Two pages of inop system messages were displayed when we began the approach.The event lasted about 45 minutes; but was so busy that it seemed to happen quickly. We were trying to complete tasks but it was challenging to complete QRH; F/A briefings; ATC communications; approach briefings; approach set up; etc in the time we had. We tried to be methodical but had to move from task to task quickly. Dispatch; ATC; MX; gate agents; and CFR were exceptional and very proactive. I don't have any suggestions about how they could have helped us any better. The Flight Attendants did an excellent job. When the cockpit lights went out; the emergency lights came on in the passenger cabin. We (pilots) were very busy trying to analyze our situation and had to tell them to stand by. The four of them got together; synced up with each other and took the time to refresh their emergency procedures and were ready for either a precautionary or emergency landing. When I was able to notify them that it would be a precautionary landing; they were well prepared; thanks to their own initiative. The takeaway for me is that we've been trained to call the flight attendants and tell them one or the other type of landing; but in this case; I did not have an immediate answer to give them. A suggestion might be that during training we should discuss a little more some scenarios where Precautionary/ Emergency landing decision is not so immediate or obvious.