title: Use variables inside :nth-child(n + x) pseudo class
body: <p>At the moment I have a snippet of LESS that will basically shift each subsequent child further down from the top:</p>
  
  <pre><code>    &amp;:nth-child(n+2) {
          top: @alertTop + 10px;
      }
  
      &amp;:nth-child(n+3) {
          top: @alertTop + 20px;
      }
  
      &amp;:nth-child(n+4) {
          top: @alertTop + 30px;
      }
  </code></pre>
  
  <p>Is there anyway to use the 'x' part of 'n+x' in the calculation so that I don't have to manually add these?</p>
  
  <p>I.e. something like:</p>
  
  <pre><code>    &amp;:nth-child(n+x) {
          top: @alertTop + (x * 5px);
      }
  </code></pre>
  
  <p>LESS/CSS only methods preferred.</p>