title: Emacs, hl-line background. How set background color with transparent?
body: <p>Windows 7, Emacs 25.1</p>
  
  <p>If I want to change background color of <strong>hl-line</strong> I do:</p>
  
  <pre><code>(set-face-background 'hl-line "#333333")
  </code></pre>
  
  <p>OK. But how I can set transparent (e.g. 50%) for <strong>hl-line</strong> background color?</p>