Top panels: $\Ds/\Dzero$ $\pt$-differential production ratios in the 0--10\% (left panel) and 30--50\% (middle panel) centrality intervals in Pb--Pb collisions at $\sqrtsNN=5.02 \TeV$ and in pp collisions (right panel) at the same centre-of-mass energy compared with theoretical calculations based on charm-quark transport in a hydrodynamically expanding QGP  and on statistical hadronisation . Bottom panels: $\Ds/\Dzero$ $\pt$-differential ratios in Pb--Pb collisions divided by those in pp collisions, in the 0--10\% (left panel) and 30--50\% (right panel) centrality intervals, compared with theoretical calculations.