Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
Se il div che non si centra è il bigdiv prova ad eliminare:
position: absolute; left: 50%; margin-left: -300px; margin-top: 150px;
ed inserisci solo:
margin: 150px auto;