Index: modules/system/system.css
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.css,v
retrieving revision 1.54
diff -u -p -r1.54 system.css
--- modules/system/system.css	11 Apr 2009 22:19:45 -0000	1.54
+++ modules/system/system.css	19 Jul 2009 05:33:20 -0000
@@ -564,3 +564,13 @@ div.password-suggestions ul {
 div.password-confirm {
   visibility: hidden;
 }
+/**
+ * Classes to ide and make content invisible.
+ */
+.hidden {
+  display: none;
+}
+.invisible {
+  height: 0;
+  overflow: hidden;
+}