Decreasing content width

Hello, I love my new Catch Inspire Pro theme and got everything running smoothly. However I would like to have just a bit more narrow look for the page. If I zoom out (- 20 %) in my browser then the page looks almost perfect. The font size is ok as it is, but I would just want the content to be less wide and have more of the beautiful white backround around the page in order to view more at once. I hope my explanation makes sense.