move login widget style to css

IPython/html/static/auth/js/loginwidget.js

@@ -19,9 +19,7 b' define(['
         }
     };
 
-    LoginWidget.prototype.style = function () {
-        this.element.find("button").addClass("btn btn-default btn-sm");
-    };
+    LoginWidget.prototype.style = function () {};
 
 
     LoginWidget.prototype.bind_events = function () {

IPython/html/static/base/less/page.less

@@ -71,6 +71,12 b' span#login_widget {'
     float: right;
 }
 
+span#login_widget > .button {
+    .btn();
+    .btn-default();
+    .btn-sm();
+}
+
 .nav-header {
     text-transform: none;
 }