diff --git a/Doc/html/style.css b/Doc/html/style.css
index 9b8ebf5ffed..3f8b3e858d9 100644
--- a/Doc/html/style.css
+++ b/Doc/html/style.css
@@ -61,6 +61,15 @@ .typelabel              { font-family: lucida, sans-serif; }
                           font-family: avantgarde, sans-serif;
                           font-size: 110%; }
 
+div.warning             { background-color: #fffaf0;
+                          border: thin solid black;
+                          padding: 0.5em;
+                          margin-left: 2em;
+                          margin-right: 2em; }
+
+div.warning .label      { font-size: 110%;
+                          margin-right: 0.5em; }
+
 .release-info           { font-style: italic; }
 
 .titlegraphic           { vertical-align: top; }