Fullcalendar - Issue changing background color of past slots with CSS

Question

I'm trying to change the background color of empty time slots that are in the past. I managed to accomplish it, but Im having an issue with the Resource Timeline View.

The horizontal lines separating the resources are hidden under the background. Note that this happens with any color, not just the one I used.

This is the css I have used :

td.fc-day.fc-day-past {
    background-color: #EEEEEE !important;
}

This is the current result :

Also, while Im here, Is there a way to not color the whole column, but just up to the last resource ?

Thanks

UPDATE I altro tried to assign a class to the past cells through the Fullcalendar configuration (the class just assigns the bg color), but nothing changed, the issue is exactly the same :

 dayCellClassNames: function (arg) {
        if (arg.isPast) {
            return ['calendar-past-event-bg']
        }
    },
    slotLaneClassNames: function (arg) {
        if (arg.isPast) {
            return ['calendar-past-event-bg'];
        }
    }