The default Google Maps InfoWindow for a map marker is very round. How do I create a custom InfoWindow with square corners?
EDIT After some hunting around, this seems to be the best option:
https://github.com/googlemaps/js-info-bubble/blob/gh-pages/examples/example.html
You can see a customised version of this InfoBubble that I used on Dive Seven, a website for online scuba dive logging. It looks like this:
There are some more examples here. They definitely don't look as nice as the example in your screenshot, however.