So, the main problem is that the component InfoBox won't allow "onChange" handlers (I presume). I need that specific one because the 3rd party component (react-datepicker) uses the "onChange" handler to set the date.
Digging through the official documentation, I've found this for the setting property "enableEventPropagation":
Propagate mousedown, mousemove, mouseover, mouseout, mouseup, click, dblclick, touchstart, touchend, touchmove, and contextmenu events in the InfoBox (default is false to mimic the behavior of a google.maps.InfoWindow). Set this property to true if the InfoBox is being used as a map label.
That's why I think it may be impossible to do it with the given date-picker, but I might be mistaken.
I've also tried setting the CSS so the date-picker component is positioned absolute to the relative parent DIV containing both the InfoBox and the date-picker, but for some reason, I cannot seem to wrap the InfoBox with the parent DIV no matter what I do. The thought process behind this is that my react-datepicker component is not really a part of InfoBox (so the "onChange" handler will work - because it works everywhere else in the app)
Any thoughts? Thanks a million!
P.S.
Setting "enableEventPropagation" to false is a default behaviour and will lead to InfoBox acting like a "read-only" label that won't allow clicks (inside its contents).