How to change the picture of a door that is past in a calendar

How to apply a different picture for each past door:

It will require to add CSS code in the CSS tab of the 'look and feel' step of your calendar.

X = day of the door,  from 1 to 31.

#calaventjouroffX.daybefore {

         background-image: url("url of your image goes here");

}

How to automatically gray out past doors images :

.daybefore {

         -webkit-filter: grayscale(100%);

         -moz-filter: grayscale(100%);

         -o-filter: grayscale(100%);

         -ms-filter: grayscale(100%);

         filter: grayscale(100%);

}

Your doors will look like this :