title: css responsive box width 90% * 95% with 5% 5% 0 5% margin
body: <p>What I'm trying to achieve is this:</p>
  
  <p><img src="https://i.stack.imgur.com/QSco5.png" alt=""></p>
  
  <p>It seems like imposible. Tried a lot of possibilities. None of them worked. This is the one I think should work.</p>
  
  <pre><code>&lt;div id="wrap"&gt;
      &lt;div id="content"&gt;hello&lt;/div&gt;
  &lt;/div&gt;
  
  html,body{
      height:100%;
  }
  
      #wrap{
          background-color:red;
          width:100%;
          height:100%;
      }
  
      #content{
          background-color:cyan;
          width:90%;
          height:95%;
          margin: 5% 5% 0 5%;
      }
  </code></pre>
  
  <p>Live: <a href="http://jsfiddle.net/vjb45/" rel="nofollow noreferrer">http://jsfiddle.net/vjb45/</a></p>