Input Error: Did not receive any STDIN - poscss-cli script

I am trying to figure out why I am getting this. I tried using this script for this create-react-app app but keep getting Input Error: Did not receive any STDIN when I run yarn run build-css or npm run build-css.

Project folder/file structure

/src/css/style.css

package.json

(note: create-react-app docs say to use build-css as the script name if you want to use your own preprocessor)

"build-css": "postcss -c postcss-options.json"

postcss-options.json (sits in the root of my app)

{
  "use": ["precss"],
  "input": "./src/css/style.css",
  "output": "./src/css/final.css",
  "local-plugins": true
}

via PositiveGuy