Where, if anywhere, is it explicitly stated that the Church may borrow and adapt heathen feasts?

I *think* I remember having read some official document of the Catholic Church (maybe even of Vatican II) explicitly stating that the Church, while establishing the Faith in a heathen area or culture, does not always need to fight the existing heathen rituals and feasts; rather, in certain cases, it may borrow and adapt these feasts, leaving many rituals but making them compatible with the Christian theology. **Now it is not my intention to discuss this particular holiday**, but just to make clear what I mean: I’ve heard people claiming that in this very fashion the Christian feast of Christmas was established, drawing its origins from the heathen feast of the Sun. (I’ve also seen people debunking this theory, though). Do I remember correctly that such a statement has been made in official documents of the Church? If so, where can it be found?