diff --git a/_layouts/default.html b/_layouts/default.html
index 0e9d6b3..b429cbb 100644
--- a/_layouts/default.html
+++ b/_layouts/default.html
@@ -178,6 +178,13 @@
         .toc-class li {
             font-size: .55rem;
         }           
+
+        .topic-optional {
+            background-color: #f9f9f9;
+            border: 1px solid #ccc;
+            padding: 10px;
+            margin-bottom: 10px;
+        }        
         
     </style>