What is the official Harvard style?
“Harvard style” is a popular name for the author-date type of parenthetical referencing.
This way of referencing does not originate from Harvard University.1) There are many variants of “Harvard style” in use, and there is no “official” Harvard Style.
If you are looking for a style called “Harvard”, you can check the many “Harvard” styles available in the Zotero Style Repository to see if there's one for your institution.
If there isn't a style for your institution, you can use the CSL Search by Example tool to find a style that matches your institution's style guide.
If you're not able to find a good match, you can request a new style.
1) Anecdotal evidence suggests the name originates with an English visitor of the Harvard University Museum of Comparative Zoology. See Chernin, Eli (1988). "The 'Harvard system': a mystery dispelled", British Medical Journal. October 22, 1988, pp. 1062–1063.