diff --git a/docs/examples/guide/dom4.css b/docs/examples/guide/dom4.css
index 7640e8d94..014142f7b 100644
--- a/docs/examples/guide/dom4.css
+++ b/docs/examples/guide/dom4.css
@@ -20,6 +20,7 @@ Button {
     content-align: center middle;
 }
 
+/* Matches the button container */
 .buttons {
     width: 100%;
     height: auto;