Reproduction: Tailwind CSS optimizer warns on Angular's ::ng-deep

README.md

::ng-deep optimizer warning reproduction

optimizeCss filters Lightning CSS warnings for :deep(), :slotted() and :global(), but not for Angular's ::ng-deep, so every Angular component stylesheet using it prints a warning block per occurrence.

npm install
npm run build

Expected: the compiled CSS, no warnings. Actual: two 'ng-deep' is not recognized as a valid pseudo-element warnings on stderr.

app.css

@import 'tailwindcss';

build.mjs

import postcss from 'postcss';
import tailwindcss from '@tailwindcss/postcss';
import fs from 'node:fs';

const file = new URL('./component.css', import.meta.url).pathname;
const result = await postcss([tailwindcss({ optimize: true })]).process(fs.readFileSync(file, 'utf8'), {
  from: file,
});
console.log(result.css);

component.css

@reference './app.css';

:host {
  ::ng-deep .some-child,
  ::ng-deep .other-child {
    @apply text-sm;
  }
}

package.json

{
  "name": "tailwind-ng-deep-warning-repro",
  "private": true,
  "type": "module",
  "scripts": { "build": "node build.mjs" },
  "dependencies": {
    "@tailwindcss/postcss": "4.3.3",
    "postcss": "8.5.6",
    "tailwindcss": "4.3.3"
  }
}