THIS PLUGIN WILL ONLY WORK IF YOU ARE USING FLYWHEEL HOSTING AND THE FLYWHEEL CDN ADD-ON.
The problem: If you use a plugin that generates dynamic CSS (for example a page builder), the Flywheel CDN add-on will not update any URLs referenced in the dynamically generated CSS. For example, a background image would use your default domain path rather than the CDN domain path.
The solution: This plugin re-writes URLs that are loaded by the WordPress wp_get_attachment_image_src function so that they are forced to use the CDN path instead.