Adding a custom background to one page

In your daily tip: https://wpmudev.com/blog/daily-tip-how-to-add-different-backgrounds-to-wordpress-pages-and-posts/

I added this plugin, but it doesn’t seem to work. So I also tried various other plugins that promised a customized background for individual pages.

The page I am trying to emulate is http://www.61ahc.org/honorroll/default.html which is, of course, an html site – converting it to wordpress.

The page I have converted to is: http://btgstudentwebsites.com/espresso/honor-roll/

However, I am unable to insert a custom background. Some of the plugins put the background up in the header. When I am using the plugin WPMUDEV seems to recommend, I have tried each choice, with the “page content” being the most logical, but nothing changes.

Thank you for your help.

Beverly