title: How to center text vertically in HTML using CSS only
body: <p>I have a very simple HTML. Due to some limitations, I cannot modify the HTML content. I want to center the text vertically only using CSS.</p>
  
  <pre><code>&lt;html&gt;
      &lt;head&gt;...&lt;/head&gt;
  
      &lt;body&gt;
          &lt;div&gt;Oops, the webpage is currently not available.&lt;/div&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>Note that the size of the HTML can be variable. </p>
  
  <p>In addition, if the text cannot be displayed in one line, it should be broken into multiple lines. </p>
  
  <p>Is it possible?</p>