Add missing CSS after merging PR 1506

ui/static/css/system.css

@@ -225,6 +225,10 @@
         --feed-has-unread-border-style: solid;
         --feed-has-unread-border-color: rgb(33 57 76);
 
+        --category-has-unread-background-color: #1b1a1a;
+        --category-has-unread-border-style: solid;
+        --category-has-unread-border-color: rgb(33 57 76);
+
         --keyboard-shortcuts-li-color: #9b9b9b;
 
         --counter-color: #bbb;