diff --git a/prototype/UI/index.html b/prototype/UI/index.html
index 97d701442..53ea32501 100644
--- a/prototype/UI/index.html
+++ b/prototype/UI/index.html
@@ -54,6 +54,7 @@
 
     .diff .category-false,
     .diff .category-true,
+    .diff .category-null,
     .diff .category-number,
     .diff .category-function_call>li>.category-identifier,
     .diff .category-function_call>li>.category-member_access>.category-identifier,