The adjective complementary means things different from each other but make a great combination.

Synonyms are completing, filling, parallel, or reciprocal.

The word origins from 1620s, from complement meaning “companion, counterpart” plus -ary. The sense of “forming a complement, mutually completing each other’s deficiencies” is attested by 1794, in reference to the calendar of the French Revolution and in reference to colors which in combination produce white light, by 1814.

These colors are very complementary.

Complementary side dishes include mashed potatoes and salads.

His singing voice is totally complementary to his father’s music writing skills.