title: The Most Efficient CSS Selector: Header Tag, Class or ID?
body: <p>As we have new elements in HTML5 (HEADER,FOOTER,SECTION...), how should we structure our CSS selectors to improve performance?</p>
  
  <pre class="lang-css prettyprint-override"><code>header {}
  header nav {}
  header nav ul li{}
  </code></pre>
  
  <p><strong>OR</strong></p>
  
  <pre class="lang-css prettyprint-override"><code>#header {}
  #header .nav{}
  #header .nav .menu{}
  </code></pre>
  
  <p>Or in some other, more efficient way?</p>