Bug 1714462 - Part 3b: Fix a CSS typo edit in panelmultiview r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D119527

browser/themes/osx/customizableui/panelUI.css

@@ -38,7 +38,7 @@ panel[type="arrow"][side="right"] {
   margin-top: -4px; /* Overrides value from panelUI.inc.css */
 }
 
-#panelmultiview .toolbaritem-combined-buttons > spacer.before-label {
+panelmultiview .toolbaritem-combined-buttons > spacer.before-label {
   width: 42px; /* 18px toolbarbutton padding + 16px icon + 8px label padding start */
 }