So, I understand that you created a background image for a TopBar to be used in by plugin.
To add this background image into the samples, you need to create a TopBar in the plugin — adding your background image to it (using the TopBar Text & Image tab). Adjust your settings to get the TopBar how you want it to look.
Then, you can export all of your Plugins using the Export Tab and selecting the JSON option.
Now, you can upload that JSON file and all images to a directory on your webserver. You’ll need to rename the file per the FAQ.
Finally, go to Global Settings and enter in the URL of the directory that has the JSON file and associated images. That URL goes into the Custom Samples URL field.
Now, you can go to the Samples Tab and your TopBar(s) will show up there.
Does this answer your question?
Bob