I am trying to add a background line image to my webpage and have inserted the following coding into my css doc

body {
background-image: url("images/background_line.gif");
background-position: 18% 18%;
background-repeat: no-repeat;

As you can see on the following page http://curvaliciousinspiration.com/blitzit/about_us.htm the image is fine on the left hand side but breaks up on the right side.
I have tried setting the image as both jpg and gif.
Any ideas what I am doing wrong please?