PostCSS - "Error: cannot find module 'tailwindcss'"

I am unable to reproduce the problem under Linux or Windows. Here’s my Windows environment.

hugo v0.88.1-5BC54738 windows/amd64 BuildDate=2021-09-04T09:39:19Z VendorInfo=gohugoio
GOOS="windows"      
GOARCH="amd64"      
GOVERSION="go1.16.7"

You might try deleting the node_modules directory, then run npm install again.

And you do not need to run npm install -g postcss postcss-cli autoprefixer. These are locally installed when you run npm install.