To turn an epub to HTML with Pandoc, you’ll need to extract the html file with pandoc.
This command extracts the files into the base directory. As well, it uses the new.min.css files for the styles in the epub.
This applies the CSS styles to the epub and extracts the images into the base directory.
pandoc -s --extract-media=. $INPUT.epub -o $OUTPUT.html -c https://cdn.jsdelivr.net/npm/@exampledev/new.css@1.1.2/new.min.css