On the sequential closure of the set of continuous functions in the space of separately continuous functions

For separable metrizable spaces $X,Y$ and a metrizable topological group $Z$ by $S(X\times Y,Z)$ we denote the space of all separately continuous functions $f:X\times Y\to Z$ endowed with the topology of layer-wise uniform convergence, generated by the subbase consisting of the sets $[K_X\times K_Y,U]={f\in S(X\times Y,Z):f(K_X\times K_Y)\subset U}$,where$U$isanopensubsetof$Z$and$K_X\subset X$,$K_Y\subset Y$ are compact sets one of which is a singleton. We prove that every separately continuous function $f:X\times Y\to Z$withzero-dimensionalimage$f(X\times Y)$ is a limit of a sequence of jointly continuous functions in the topology of layer-wise uniform convergence.