background image url

I’m unable to use a theme’s bg-pattern.png for my image object after applying the custom css attribute within the .wp-caption class. I believe the problem lies within the background url since applying a generic background colour worked. It looks like the plugin applies the custom lines in-line using a style id simpler-css-style but I don’t know how to re-direct it to the proper path. Please help!

https://www.ads-software.com/extend/plugins/imporved-simpler-css/