Add this code to the Custom CSS field on the Appearance tab of your Event Calendar widget’s settings:
.fc-day-past .fc-daygrid-event {
background-color: #ccc !important;
}
Guys, if this code was helpful, please drop us a line in the comments 
Add this code to the Custom CSS field on the Appearance tab of your Event Calendar widget’s settings:
.fc-day-past .fc-daygrid-event {
background-color: #ccc !important;
}
Guys, if this code was helpful, please drop us a line in the comments