Centering The Div
With the new Div created and on your page, find the “Manage Styles" panel. This is usually the bottom right panel in the Expression Web interface.
Select the “New Style" option in this panel and wait for the new window to load. There are a few different selections and customizations you are going to need to fulfill to ensure the web page gets centered.
Enter a name for the Div you have just created and check the box beside it labelled “Apply New Style To Document Selection." Ensure that the CSS you are working with is in the .CSS field, then direct your attention to the “Position" tab in the window.
Click on this tab and you will be presented with various fields where you can define the height, width, etc. You must set a width for the Div you just created, preferably 800.
You will also need to set the height, which is yours to determine. Just remember, the height you put here will be the height of your web page; so ensure it is large enough length wise.
Once you are done defining these fields, find the “Box" tab. This provides you with padding and margin options. A margin is needed to center the page. For the top and bottom, select “0." For the left and right margins, select “Auto" from the drop-down list.
Click “Okay" and wait for the window to close.