Bootstrap Grid System: How to make container center

Bootstrap Grid System: How to make container center

I am using twitter bootstrap to code a site. This is my first website
using bootstrap and even though I have read the documentation well I am
stumbling with a few things.
Firstly, I am unable to center vertically my two divs '.coming-soon' and
'.main-content'. The webpage can be viewed at:
http://www.domainandseo.com/bootstrap/index.html
My custom CSS file can be viwed at :
http://www.domainandseo.com/bootstrap/css/style.css
Also another thing is that I want the width of my coming soon to be equal
to 640px for larger screens and scale down when the screen is smaller.
Using the grid system I have given it a class of span7 which equals to
670px. Any way to decrease the 30px (preferably in a way that it scales
down eqaully when screen size decreases).