[Plugin: OptionTree] Using the 'Background' option

Can anyone explain how to integrate the ‘background’ option in a theme? While I love this theme, and have no issues with the most part, the whole custom css section escapes me.

I’ve added this to dynamic.css, with no results:

body {
  {{custom_bg_css}}
}

I also called the file ‘dynamic.css’ in the header manually, but the database won’t populate the css fields. When I view the source, it picks up dynamic.css, and the body tag, but all I get are empty tags:

body { }

I would really appreciate it if someone could tell me how to use the custom css option in this plug-in.

Thanks in advance.

https://www.ads-software.com/extend/plugins/option-tree/