Google Maps: How to add HTML elements to specific coordinates?

you can use custom overlays - https://developers.google.com/maps/documentation/javascript/customoverlays for that

As roman said, you can create a custom javascript object which implements GOverlay.

Here's an example from another S.O. question where the guy wanted to insert an SVG on top of a google map. However I am pretty sure you could use his solution to just insert HTML.