fix control sidebar top padding (#1525)

build/less/control-sidebar.less

@@ -24,7 +24,7 @@
   padding-top: @navbar-height;
   z-index: 1010;
   // Fix position after header collapse
-  @media (max-width: @screen-sm) {
+  @media (max-width: @screen-xs-max) {
     padding-top: @navbar-height + 50;
   }
   // Tab panes