Ul effects for past and days outside of month
Again looking at our finished product, you'll notice that any day which is in the past,
so in other words anything before today's date, it has this transparency sort of effect on it.
That's just a visual indication to any user that, oh hey, this is the past.
So you'll notice again if we inspect the the DOM here that any day in the past has this past class.
So let's add that to ours as well.
So adding to our class object on calendar-day