  An efficient way to study the QCD phase diagram at small finite density is to
extrapolate thermodynamical observables from imaginary chemical potential. The
phase diagram features a crossover line starting from the transition
temperature already determined at zero chemical potential. In this work we
focus on the Taylor expansion of this line up to $\mu^4$ contributions. We
present the continuum extrapolation of the crossover temperature based on
different observables at several lattice spacings.
