Set text width and align for a page

Hey,

I need to set the width of the text and align it to the right, however I have difficulty doing this without affecting any of the other page elements.

The last time, for example, some CSS modifications changed the header, menu bar as well as the paralax image.

This is only for this page. I do not necessarily want the same text width and alignment for all my pages.

Here is my page right now:
http://www.matthewgibbonswriting.com/?page_id=2648&preview=true&preview_id=2648&preview_nonce=2c46ff7613

Any help?