Index: theme.php
===================================================================
--- theme.php	(revision 21544)
+++ theme.php	(working copy)
@@ -1158,7 +1158,7 @@
 	}
 ?>
 <style type="text/css" id="custom-background-css">
-body.custom-background { <?php echo trim( $style ); ?> }
+<?php echo apply_filters( 'custom_background_selector', 'body.custom-background' ) ?> { <?php echo trim( $style ); ?> }
 </style>
 <?php
 }