--- a/browser/themes/shared/incontentprefs/preferences.inc.css
+++ b/browser/themes/shared/incontentprefs/preferences.inc.css
@@ -508,17 +508,17 @@ description > html|a {
   text-align: center;
   padding-left: 11px;
   padding-right: 11px;
   margin: 0;
   min-width: 0;
 }
 
 .fxaAccountBoxButtons > button:first-child {
-  margin-right: 14px !important;
+  margin-inline-end: 14px !important;
 }
 
 .fxaSyncIllustration {
   width: 231px;
   list-style-image: url(chrome://browser/skin/fxa/sync-illustration.png)
 }
 
 #fxaLoginStatus[hasName] #fxaEmailAddress1 {