title: How to use CSS to make this works on retina screen?
body: <p>Code is like:</p>
  
  <pre><code>&lt;a href="http://localhost/link-a"&gt;&lt;img src="a.png"&gt;&lt;/a&gt;
  </code></pre>
  
  <p>The image file a.png is 100x100 but on retina screen it's very ugly so I can generate a 2x PNG file. But how do I make it work in this HTML code?</p>