the small-btn class doesn't exist anymore

less/navbar.less

@@ -19,7 +19,7 @@ nav, .navbar-link:hover, .pagename {
 	font-size: 14px;
 }
 
-button.btn.close.small-btn {
+button.btn.close.btn-sm {
 	background: #000;
 	visibility: hidden;
 	float: right;