title: How to check the maximum number of selectors in stylelint?
body: <p>I need to check that there is one root class in one file.
  Is it possible? </p>
  
  <pre><code>// Error
  .a { }
  .b { }
  </code></pre>
  
  <p>Expected</p>
  
  <pre><code>// Success
  .a {}
  </code></pre>