diff --git a/chrome/content/zotero-platform/win/overlay.css b/chrome/content/zotero-platform/win/overlay.css
index 4d46ca15df..591d8ed3df 100644
--- a/chrome/content/zotero-platform/win/overlay.css
+++ b/chrome/content/zotero-platform/win/overlay.css
@@ -10,7 +10,7 @@
 #zotero-pane #zotero-toolbar {
 	-moz-appearance: none !important;
 	margin-top: -3px;
-	border-bottom-color: var(--theme-border-color);
+	border: 1px solid var(--theme-border-color);
 }