classname for theming calendar property in style.css?

[thelazt16]

I know I can do some styling inside the config but it pretty limited and quite annoying to do. I wanted to know if I can style the calendar tooltip inside style.css instead.
I can't find a way to make the debug mode (GTK_DEBUG=interactive waybar) to work with the tooltip since I can't use the element picker and it doesn't seems to show up in the objects tab nor the CSS node dropdown.