Set variable for FullCalendar border colour so that we don't have to select every element on its own

frontend/src/app/features/calendar/wp-calendar/wp-calendar.sass

@@ -1,4 +1,6 @@
 .op-wp-calendar
+  --fc-border-color: #cccccc
+
   // Ensure some sane min-height
   // to ensure fullcalendar has something to render
   min-height: 200px

frontend/src/global_styles/content/modules/_team_planner.sass

@@ -13,6 +13,8 @@
         display: none
 
 .op-team-planner
+  --fc-border-color: #cccccc
+
   &--calendar_empty
     .fc-scrollgrid-section-body,
     .fc-scrollgrid-section-footer

frontend/src/global_styles/vendor/_full_calendar.sass

@@ -10,15 +10,11 @@
     .fc-col-header-cell-cushion
       padding: 12px 16px
 
-    .fc-timeline-lane,
-    .fc-timeline-slot-lane
-      border-color: #c1c1c1
-
     .fc-timeline-lane-frame
       padding: 4px 0
 
     .fc-resource-timeline-divider
-      width: 1px
+      width: 0
       background: none
       border: none
       cursor: unset