MDL-40975 Theme: Dim the modicon when an activity is disabled

theme/bootstrapbase/less/moodle/course.less

@@ -71,6 +71,15 @@
             right: 0;
             top: 0;
         }
+
+        .activityinstance {
+            .dimmed {
+                img.activityicon {
+                  opacity: 0.5;
+                  filter: alpha(opacity=50);
+                }
+            }
+        }
     }
 
     .filler {