Use less2 in sframe drive

customize.dist/src/less2/include/dropdown.less

@@ -1,4 +1,5 @@
 @import (once) "./colortheme.less";
+@import (once) "./tools.less";
 
 /* The container <div> - needed to position the dropdown content */
 .dropdown_main () {
@@ -17,7 +18,7 @@
                 margin-left: 5px;
             }
             * {
-                .unselectable();
+                .tools_unselectable();
                 cursor: default;
             }
         }