It would be appropriate to put "centrifugal force" in quotes, since it is a bit of a fiction.

In a "Classical*" representation of an atom, the negative electrons spin around the positive nucleus like a weight on a string. In this model, the 'opposite reaction' to the centrifugal force is the electrostatic attraction between the electron and the nucleus. Since the familiar atoms are quite stable, the two forces are already in balance, and the electric charges are in balance. But Gravity still operates.

In a "quantum" model of the atom, the electron is not a weight at a single point in space, but an extended wave function which is the size of an atom. This represents the probability that you will find an electron at that point in space. There is no point mass which is whizzing around, and no centrifugal force needed to counterbalance it. But Gravity still operates.

*Physicists don't have a very old culture. "Classical" means more than 100 years old...