title: How to make div width almost 100%
body: <p>I have such a html code:</p>
  
  <pre><code>&lt;div id="outer"&gt;
      &lt;div id="inner"&gt;&lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>How can I make #inner div to have width 100% of #outer but minus 10px? </p>
  
  <p>Here is my css:</p>
  
  <pre><code>#outer {
      width: 100%;
      max-width: 500px;
  }
  </code></pre>