Support tailwind v4 in Angular Unit Tests

[jlanssie]

What version of Tailwind CSS are you using?

v4.1.10

What build tool (or framework if it abstracts the build tool) are you using?

postcss v8.5.6, angular v19.2.0

What version of Node.js are you using?

v22.13.1

What browser are you using?

n/a

What operating system are you using?

macOS

Reproduction URL

n/a

Describe your issue

When building a new Angular project according to the Tailwind documentation at Tailwind, it is impossible to run unit tests.

When trying to run a unit test, the following error is thrown:

/Users/jlanssie/.nvm/versions/node/v22.13.1/bin/node /private/var/repos/personal/angular-app/node_modules/@angular/cli/bin/ng test angular-app --karma-config /Applications/IntelliJ IDEA.app/Contents/plugins/karma/js_reporter/karma-intellij/lib/intellij.conf.js --source-map
/private/var/repos/personal/angular-app/node_modules/@angular-devkit/architect/node_modules/rxjs/dist/cjs/internal/util/reportUnhandledError.js:13
            throw err;
            ^

Error: It looks like you're trying to use `tailwindcss` directly as a PostCSS plugin. The PostCSS plugin has moved to a separate package, so to continue using Tailwind CSS with PostCSS you'll need to install `@tailwindcss/postcss` and update your PostCSS configuration.
    at We (/private/var/repos/personal/angular-app/node_modules/tailwindcss/dist/lib.js:35:2121)
    at getStylesConfig (/private/var/repos/personal/angular-app/node_modules/@angular-devkit/build-angular/src/tools/webpack/configs/styles.js:106:66)
    at async Promise.all (index 1)
    at async generateWebpackConfig (/private/var/repos/personal/angular-app/node_modules/@angular-devkit/build-angular/src/utils/webpack-browser-config.js:74:22)
    at async generateBrowserWebpackConfigFromContext (/private/var/repos/personal/angular-app/node_modules/@angular-devkit/build-angular/src/utils/webpack-browser-config.js:129:20)
    at async initializeBrowser (/private/var/repos/personal/angular-app/node_modules/@angular-devkit/build-angular/src/builders/karma/browser_builder.js:109:24)

Node.js v22.13.1

Process finished with exit code 1

[thecrypticace]

Can you provide a reproduction project that we can test?