diff --git a/chrome/content/zotero/overlay.js b/chrome/content/zotero/overlay.js
index 3869e2df6c..d1029baf29 100644
--- a/chrome/content/zotero/overlay.js
+++ b/chrome/content/zotero/overlay.js
@@ -137,6 +137,9 @@ var ZoteroPane = new function()
 		
 		if (Zotero.isMac) {
 			document.getElementById('zotero-tb-actions-zeroconf-update').setAttribute('hidden', false);
+			document.getElementById('zotero-pane').setAttribute('platform', 'mac');
+		} else if(Zotero.isWin) {
+			document.getElementById('zotero-pane').setAttribute('platform', 'win');
 		}
 		
 		//Initialize collections view
diff --git a/chrome/skin/default/zotero/overlay.css b/chrome/skin/default/zotero/overlay.css
index 14ae535f3c..06e1329bdb 100644
--- a/chrome/skin/default/zotero/overlay.css
+++ b/chrome/skin/default/zotero/overlay.css
@@ -25,12 +25,12 @@
 }
 
 /* these are hacks do display a window separator in full screen mode on OS X */
-window[activetitlebarcolor] #zotero-pane[fullscreenmode="true"]
+window #zotero-pane[fullscreenmode="true"][platform="mac"]
 {
 	border-top: 1px solid #A3A3A3;
 }
 
-window[active="true"][activetitlebarcolor] #zotero-pane[fullscreenmode="true"]
+window[active="true"] #zotero-pane[fullscreenmode="true"][platform="mac"]
 {
 	border-top: 1px solid black;
 }