Upper panels: invariant-mass distribution of opposite-sign lepton pairs from the same event (black points) and mixed events (red histograms) at midrapidity (left) and forward rapidity (right) in \PbPb collisions at \fivenn. Lower panels: invariant-mass distribution after the background subtraction with the event-mixing technique. The fit curves, shown in red, represent the sum of the signal and background shapes and the blue curves correspond to the residual background.