I’m receiving the same error trying to deploy this tailwind starter theme on Cloudflare Pages.
Error: error building site: POSTCSS: failed to transform "css/styles.css" (text/css). Check your PostCSS installation; install with "npm install postcss-cli". See https://gohugo.io/hugo-pipes/postcss/: binary with name "npx" not found
The theme works just fine locally.
The original Github issue [#9730] reported the following
It looks like any errors with the npx call get handled as if postcss is not supported.
I’m out of my depth here and wondering where I might begin troubleshooting? I’ve set environment variables to make sure the correct version of Hugo is being used. I’ve got other Hugo sites deploying fine on CFP, but they are not using postcss.