How to vertically center a fixed height theme?

Hey, I’ve changed the suffusion theme’s css to give it a fixed height on my test server, but now I need to center it vertically. I’m assuming you need to edit the #wrapper, but everything I’ve tried has just messed the alignment up completely, so I’ve just gone back to the default. Test site is https://test.adept.co.za/www.fairhills.co.za/

#wrapper {
width: 1000px;
margin: 20px;
border: 1px solid #008000;
background-color: #EDF3E6;
padding: 10px;
}

Someone please help.