A321 First Officer reported landing safely after experiencing loss of green hydraulic system fluid.

Narrative

On descent into ZZZ on the ZZZZZ arrival we experienced a loss of hydraulic fluid pressure descending through FL240 over ZZZZZ1. We received the ECAM 'HYD G RSVR LO LVL. We announced the ECAM; I remained pilot flying and took over ATC communications. The Captain ran the ECAM procedure; coordinated with dispatch/cabin crew and kept passengers informed. As time allowed during this high workload event; we briefed each other on any status updates and changes that had occurred. We [notified] ATC and dispatch. We continued an otherwise normal descent. We were vectored off of the arrival and set up for an ILS approach to RW XXR at ZZZ. Once all ECAM procedures were complete and landing distance procedures applied; we continued on the approach for RW XXR. We followed the procedure for manual gear extension; and configured early to account for slower flap/slat movement. We transferred controls and the captain completed an uneventful landing. We rolled to the end of the runway and were able to make a slow; cautious turn off on taxiway 1. We paused on the taxiway to evaluate the situation. We had an indication of HYDR pressure in the green system that was below the normal range; but above the Amber Caution range; where it had been in the air. Given no other abnormal indications; we elected to turn the green engine 1 pump back on and turn the Power Transfer Unit (PTU) switch back on. All indications at this point were within normal parameters and we elected to taxi to the gate. We parked uneventfully and passengers deplaned. We coordinated with maintenance at the gate and informed them of the event. They confirmed that we had experienced a loss of hydraulic fluid likely due to a compromised diaphragm seal. The loss of fluid was incomplete; maintenance personal estimated roughly 2 gallons remained. Fluid was still visibly leaking from the accumulator and a puddle was on the ground in the area. All in all; the outcome was successful. I think good CRM was a major factor in completing a safe landing. The captain exercised excellent leadership effectiveness by delegating duties. We both did a good job of workload management in a very high workload event in busy airspace. We communicated effectively and kept each other informed as we worked through the situation. I am a new hire pilot. This was my second trip upon completion of IOE. I think my recent experience in the simulator also helped contribute to a good outcome and I think it indicates the quality of our training program. We followed all SOPs and ECAM procedures effectively and completed a crew debrief using CRM/TEM (Threat and Error Management) skills afterwards; exactly as we are trained to do."