have you looked in the content of the downloaded app.css, it seems quite small ?
yea i did. 
The response does not have anything related to Tailwind
and why you use npm to build the assets, you have esbuild for that job
correct. npm is only used to fetch additional packages, like React
assets are being built by esbuild itself.
I forgot to add this part in the actual question. but here is my alias for mix assets.deploy:
# mix.exs
"assets.deploy": ["tailwind default --minify", "esbuild default --minify", "phx.digest"]
