Add support for a highlighted navigation counter

Signed-off-by: Joas Schilling <coding@schilljs.com>

core/css/apps.scss

@@ -435,6 +435,13 @@ kbd {
 			font-size: 9pt;
 			line-height: 44px;
 			padding: 0 12px; /* Same padding as all li > a in the app-navigation */
+
+			span.highlighted {
+				padding: 2px 5px;
+				border-radius: 10px;
+				background-color: $color-primary;
+				color: $color-primary-text;
+			}
 		}
 	}