How to specify CSS class for GTK widgets in v3?

[MonstrousOgre]

Basically, I'm trying this

   <Gtk.Calendar
      expand
      class={"calender-menu-widget"}
      showDayNames
      showDetails={false}
      showHeading
    />

It gives the error "No property class on GtkCalendar". Is there anyway to do this?

[Aylur]

are you sure you are on v3?

[MonstrousOgre]

Sorry I didn't see this earlier. The output of ags -v is

ags version 3.1.0

I'm able to specify classes on Astal widgets just fine but not on GTK widgets.