diff --git a/src/browser/base/content/zen-styles/zen-browser-ui.css b/src/browser/base/content/zen-styles/zen-browser-ui.css
index 45cb3021d..c86d168eb 100644
--- a/src/browser/base/content/zen-styles/zen-browser-ui.css
+++ b/src/browser/base/content/zen-styles/zen-browser-ui.css
@@ -52,7 +52,7 @@
   flex-direction: row;
 }
 
-#titlebar-buttonbox-container {
+.titlebar-buttonbox-container {
   height: 100%;
 }