title: Remove duplicate CSS declarations across multiple files
body: <p>I'm looking to remove duplicate CSS declarations from a number of files to make implementing changes easier. Is there a tool that can help me do that?</p>
  
  <p>Right now I'm faced with something like this:</p>
  
  <pre><code>styles.css
  #content {
  width:800px;
  height:1000px;
  background: green;
  }
  
  styles.game.css
  #content {
  width:800px;
  height:1000px;
  background: blue;
  }
  </code></pre>
  
  <p>And I want this:</p>
  
  <pre><code>styles.css
  #content {
  width:800px;
  height:1000px;
  background: green;
  }
  
  styles.game.css
  #content {
  background: blue;
  }
  </code></pre>
  
  <p>The total number of lines across all files is well over 10k, so techniques that rely on manual editing aren't an option.</p>