Added more style for major warnings.

Doc/html/style.css

@@ -61,6 +61,15 @@ var                     { font-family: times, 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; }