Look at Node-RED the initialization log. It will show you what is your static file. At the time of this writing I am using windows and this is how the initialization log looks like.
The static path is: C:/Users/OCM/.node-red/static
The target image is on folder: C:/Users/OCM/.node-red/static/nri
Therefore I configure the URL statement this way:
background-image: url("/nri/cluster-fuel.png");
The initialization log also tells you where you can find the settings.js file. In my case:
Copyright OpenJS Foundation and Node-RED contributors. All rights reserved. The OpenJS Foundation has registered trademarks and uses trademarks. For a list of trademarks of the OpenJS Foundation, please see our Trademark Policy and Trademark List. Trademarks and logos not indicated on the list of OpenJS Foundation trademarks are trademarks™ or registered® trademarks of their respective holders. Use of them does not imply any affiliation with or endorsement by them.
The OpenJS Foundation | Terms of Use | Privacy Policy | OpenJS Foundation Bylaws | Trademark Policy | Trademark List | Cookie Policy
