title: Change box size when resize window with css
body: <p>I have this simple website</p>
  
  <pre><code>&lt;div style=" position: relative; margin-right: 40px;"&gt;
      &lt;div style="float: left; width: 100px; position: relative;"&gt;Middle Stuff&lt;/div&gt;
      &lt;div style="float: right; width: 200px; position: relative; margin-right: 40px;"&gt;Right Stuff&lt;/div&gt;
      &lt;br style="clear: left;" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>and I want that the middle stuff-box-width grow up when I resize the window so that between the middle stuff-box and the right stuff-box is no empty content.</p>
  
  <p><img src="https://i.stack.imgur.com/baXTV.png" alt="Here can you see what I want"></p>
  
  <p>How can I get this "effect"?</p>