Extend css with less

Question

I'm trying to add my own less definition based on glyphicon in bootstrap. So I have this .less file:

/// <reference path="../Content/bootstrap.css" />

@import (reference) "../Content/bootstrap.css";

.status-ok-icon {
    .glyphicon;
    .glyphicon-ok;
    color: green;
}

But the compiler output returns:

.glyphicon is undefined on line 6 in file '/SiteCSS/client.less':
  [5]: .status-ok-icon {
  [6]:     .glyphicon;
       ----^
  [7]:     .glyphicon-ok;

Anybody could help me point out the mistake? I'm using less for the first time.