But today I was able to really appreciate the use of custom widgets. As you can see, sometimes I have too many labels in a MonthCell, they don’t fit inside. In this case gnome-calendar has a button that you press, a popover window appers, and you can see all events.
So today I was playing with Gcal.MonthPopover, it’s still in the works, but here’s what I managed to do:
I will have to add all labels to the popover, but it’s working! The Gcal.MonthPopover is also pretty easy to instantiate and use.
I’m happy with the result. Thank you everybody who helped me: thank you Zander for making a first comment, special thanks to Emmanuele and Nicola for your enormous help, and thanks Jason for participating! I love you all 
, and you are awesome!