Vertical-align:middle on #page

Hi guys!
I created a TwentyEleven child theme, and I’m trying to vertically center the main <div> (#page). Here’s the website: http://compagniaoltreconfine.com/beta/

As you can see I’m trying with these CSS:
body, html, #wrapper { width: 100%; height: 100% }
#wrapper { display: table }
#main { display: table-cell; vertical-align: middle !important }

And I added a <div> wrapper before #page.

This method doesn’t work.
It’s 5 days I’m trying to achieve this, please help me!! 😀

P.S.: Don’t suggest me to use position:absolute and negative margins because my website doesn’t have a fixed height