Run an NPM script inside every package in an NX project's library - npm

Question

I'm using NX to manage a React design system mono-repo. I want to create my components within an NX Library and am currently looking into creating a Node package which will run the CSS for each component through PostCSS to get it production ready.
I've tested my PostCSS Node package in isolation and I know it's doing what I need it to to the files, however I'm having trouble working out how to configure the NX repo to run an NPM script in each component's package.json. A component such as my Button component has a package.json like so:
{
"name": "css-components-button",
"version": "0.1.0",
"main": "index.js",
"license": "MIT",
"scripts": {
"prepack": "tools-postcss 'lib/**/*.css' dist/"
},
"dependencies": {
"tools-postcss": "file:.yalc/tools-postcss"
}
}
In the CSS Components Library the project.json file looks like this:
{
"name": "css-components",
"sourceRoot": "libs/css-components/src",
"projectType": "library",
"tags": [],
"targets": {
"lint": {
"executor": "#nrwl/linter:eslint",
"outputs": ["{options.outputFile}"],
"options": {
"lintFilePatterns": ["libs/css-components/**/*.{ts,tsx,js,jsx}"]
}
},
"build": {
"executor": "#nrwl/rollup:rollup",
"outputs": ["{options.outputPath}"],
"options": {
"outputPath": "dist/libs/css-components",
"tsConfig": "libs/css-components/tsconfig.lib.json",
"project": "libs/css-components/package.json",
"entryFile": "libs/css-components/src/index.ts",
"external": ["react/jsx-runtime"],
"rollupConfig": "#nrwl/react/plugins/bundle-rollup",
"compiler": "babel",
"assets": [
{
"glob": "libs/css-components/README.md",
"input": ".",
"output": "."
}
]
}
},
"test": {
"executor": "#nrwl/jest:jest",
"outputs": ["{workspaceRoot}/coverage/{projectRoot}"],
"options": {
"jestConfig": "libs/css-components/jest.config.ts",
"passWithNoTests": true
}
},
"prepack": {
"executor": "#nrwl/workspace:run-script",
"options": {
"script": "prepack"
}
}
}
}
In particular I've added a "prepack" custom target which I'm trying to use to run a "prepack" NPM script in each component's package.json. Currently when I run nx run css-components:prepack in the Terminal I get **error Command "prepack" not found.**
Would really appreciate some help with this. Any ideas?