This is not the fixed I hoped for, but the JS generates so many empty `<span>` tags that I cannot get rid of, that it is not possible to style this "from the outside", which is unfortunate.
Remove Tailwind Compatibility Mode and PostCSS. Install newest tailwind and configure it to use JIT-Mode. Setup npm run scripts to run TailwindCSS CLI and Parcel in parallel. The Tailwind index.css and all .html/.ts files are scanned live and generated to /css/index-tailwind-output which is in turn included in index.html.