see https://tinyurl.com/NicerAppWebOS-bgs-favs-3 and 'Downloading more backgrounds.png' in this folder.

download the zip file into .../NicerAppWebOS/siteMedia/backgrounds, unzip it right there.

then delete all files matching .../NicerAppWebOS/siteCache/*.json
and the website will find the new backgrounds when viewed again in the browser.