 <p>Since you're using percentages for both <code>top</code> and <code>margin-top</code>, you can combine them, and simply use <code>top: 10%</code>.</p> <p>See this demo: <a href="http://jsfiddle.net/jackwanders/DEn6r/3/" rel="nofollow">http://jsfiddle.net/jackwanders/DEn6r/3/</a></p> <p>Also, if you'd like to drop the negative left margin, you can use this trick to center the div horizontally:</p> <pre><code>#inside { position: absolute; width: 300px; height: 80%; top: 10%; left: 0; right: 0; // set left and right to 0 margin: 0 auto; // set left and right margins to auto background: white; } </code></pre>