Add a fixed background while scrolling for single page

Hey all,

Im trying to add a fixed image to the background of a single page on my site. I want it for when the user scrolls down, the image stays in place. I found a tutorial online, but it doesn't seem to be working on my site... It might be perhaps because I am using 7.0. 

https://thirtyeightvisuals.com/blog/fixed-background here is the link to the tutorial.

 I attached the image I am wanting to use for the background.