Fix minor visual issue

themes/learn2/css/custom.css

@@ -45,6 +45,11 @@ Put your custom CSS in this file.
     opacity: 1; /* something firefox fix */
 }
 
+/* very thin bar between last topic and clear history */
+#sidebar hr {
+    border-bottom: 1px solid #47314f
+}
+
 /* full content */
 body {
     background: #111111;