title: DotLess not importing CSS file
body: <p>I'm trying to use <a href="http://www.dotlesscss.org/" rel="nofollow">DotLess</a> in a project, but I'm running into an issue I cannot seem to resolve. I am trying to extend a pre-existing CSS file (which is actually from JQuery UI) by using a LESS mixin in my own custom file. </p>
  
  <p>In jquery-ui-1.8.20.custom.css:</p>
  
  <pre><code>.ui-state-hover, .ui-widget-content .ui-state-hover, .ui-widget-header .ui-state-hover, .ui-state-focus, .ui-widget-content .ui-state-focus, .ui-widget-header .ui-state-focus { border: 1px solid #79b7e7; background: #d0e5f5 url(images/ui-bg_glass_75_d0e5f5_1x400.png) 50% 50% repeat-x; font-weight: bold; color: #1d5987; }
  </code></pre>
  
  <p>And the relevant portions of my custom.less file:</p>
  
  <pre><code>@import "./jquery-ui-1.8.20.custom.css";
  
  .sortable-list li:hover {
      .ui-state-hover;
  }
  </code></pre>
  
  <p>When I try to compile this with the following DotLess command:</p>
  
  <pre><code>.\dotless-compiler -m [LESS_FILE_PATH]\custom.less .\custom.generated.css
  </code></pre>
  
  <p>I receive the following error message:</p>
  
  <pre><code>.ui-state-hover is undefined on line 92...
  [91]: .sortable-list li:hover {
  [92]:     .ui-state-hover;
    ----^
  [93]: }[Done]
  </code></pre>
  
  <p>a) Does anyone know if I'm missing argument(s) to the command line compiler? (<em>Documentation</em> for it would really be nice...)</p>
  
  <p>b) If not, is there some inherent shortcoming of LESS that cannot handle the situation I have described? Extending existing CSS files that you cannot touch seems like an extremely common use case.</p>