use moz-appearance bg for pane, window, etc for backgrounds in dialogs. makes pref panels look much better. r=andreww/sr=ben/a=asa. bug#134720

themes/classic/global/mac/global.css

@@ -61,6 +61,7 @@ window,
 page,
 dialog,
 wizard { 
+  -moz-appearance: dialog;
   background-color: -moz-Dialog;
   color: -moz-DialogText;
   font: message-box;

themes/classic/global/mac/groupbox.css

@@ -44,6 +44,7 @@ groupbox {
 }
 
 caption {
+  -moz-appearance: dialog;
   margin: 0px 6px 2px 6px;
   padding: 0px 3px;
   background-color: -moz-Dialog;