title: External Style Sheet is not valid in AMP Pages
body: <p>I am converting my HTML page into AMP Pages. 
  I have seen test url <a href="https://validator.ampproject.org/#" rel="nofollow noreferrer">https://validator.ampproject.org/#</a>. This page is validate from AMP. </p>
  
  <p><strong><em>Screen Shot for Help:</em></strong>
  <a href="https://i.stack.imgur.com/wcDLH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wcDLH.png" alt="enter image description here"></a></p>
  
  <p>But When I used External Css.  </p>
  
  <pre><code>&lt;link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.98.0/css/materialize.min.css"&gt;
  </code></pre>
  
  <p>Then It will fail.</p>
  
  <p><strong><em>Screen Shot For help.</em></strong>
  <a href="https://i.stack.imgur.com/sXyIl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sXyIl.png" alt="enter image description here"></a></p>
  
  <p>Then how can I access materialize css file. Because I am using Materialize Ui framework  in my website.</p>
  
  <p>But I have read also about</p>
  
  <pre><code> &lt;style amp-custom&gt; &lt;/style&gt;
  </code></pre>
  
  <p>SO AMP validate page suggest include inline css in amp-custom.
  But materialize css is so long. It will break in some mobile browsers. Because <a href="https://github.com/ampproject/amphtml/issues/4555" rel="nofollow noreferrer">https://github.com/ampproject/amphtml/issues/4555</a></p>
  
  <p>If anybody have some idea then please share.</p>