Relative systematic uncertainty from the background uncertainty of $10^{-4}$ on the corrected dielectron yield in bins of $m_{\rm {ee}}$ and $p_{\rm {T,ee}}$ for $0.2 < p_{\rm T,e} < 10 $GeV/$c$ and $|\eta_{\rm e}| < 0.8$ in the 10% most central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV.