How does a Lewis acid-base reaction form a covalent bond?

In the Lewis theory of acids and bases, a covalent bond is formed through the interaction between an electron-pair acceptor and an electron-pair donor.1

A Lewis acid is defined as a chemical species capable of accepting an unshared pair of electrons, while a Lewis base is a species that provides that electron pair. During the reaction, the base donates its electron pair to the acid, resulting in the formation of an addition compound, or adduct, in which the two species are joined by a shared electron pair.213

This process is distinct from oxidation-reduction reactions, where electrons are transferred completely from one species to another. In a Lewis acid-base reaction, the electron pair remains associated with the base but is shared to create a covalent link with the acid. If both reactants are uncharged, the resulting bond is often referred to as a coordinate or semipolar bond.13