page & post margins adjustment (left and right margins)

Hello,

I wanted to write with a question concerning the adjustment of the left and right margins for all of the pages and posts of my site. My issue is that each line of text on each of my pages and posts is very long and I would like to shorten all of them by increasing the margins on the left and right sides of every page/post so that each paragraph of text is more narrow and less wide.
My understanding is that I need to make adjustments within the Stylesheet (style.css) of the theme editor for the Oblique theme, but I do not know what to do. Any assistance that you might be able to provide would be greatly appreciated!

Thank you!

The page I need help with: [log in to see the link]