diff --git a/IPython/html/static/notebook/js/menubar.js b/IPython/html/static/notebook/js/menubar.js
index f7d5a81..b3b2eae 100644
--- a/IPython/html/static/notebook/js/menubar.js
+++ b/IPython/html/static/notebook/js/menubar.js
@@ -52,7 +52,6 @@ define([
 
     MenuBar.prototype.style = function () {
         var that = this;
-        this.element.addClass('border-box-sizing');
         this.element.find("li").click(function (event, ui) {
                 // The selected cell loses focus when the menu is entered, so we
                 // re-select it upon selection.
diff --git a/IPython/html/static/notebook/less/menubar.less b/IPython/html/static/notebook/less/menubar.less
index 99f1ba7..69ea262 100644
--- a/IPython/html/static/notebook/less/menubar.less
+++ b/IPython/html/static/notebook/less/menubar.less
@@ -2,6 +2,7 @@
   margin-top: 0px;
   margin-bottom: -19px;
   position: relative;
+  .border-box-sizing();
 
   .navbar {
     border-top: 1px;