`loader` option in the `application` builder does not work for *.css files.

使用 angular.json、main.ts、ng build 和 ng serve 以及 .css loader 设置，通过最小示例重现该问题。首先跟踪 application builder 对从 TypeScript 导入的 CSS 的处理方式，然后验证生成的 CSS 已由 served application 加载，并确认在 build 和 serve 模式下行为一致。

Command

build, serve

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

When trying to import a *.css file inside a *.ts with the following syntax:

import './my-styles.css';

The built css file is never loaded into the application.
I was pointed out in https://github.com/angular/angular-cli/issues/27414 that I should use the new loader however that does not seem to work.

angular.json:

"loader": {
  ".css": "file"
}

ng serve output:

This would be useful in order to support third party libraries that use this kind of imports like monaco-editor.

Vite already handles this when we run ng serve --prebundle=true and it works when a library uses this imports, but it does not work with ng build or ng serve --prebundle=false.
Also esbuild is able to handle the import (https://esbuild.github.io/content-types/#css-from-js) and generate a css bundle for all the css imports that it finds in a entry point, for example I can see it generating a main.css file:

However, the css bundle outputted to the ./dist/** folder it is never loaded onto the app.

Minimal Reproduction

ng new my-app
cd ./my-app

Create a *.css file called "import-styles.css"
Import the file above into the main.ts or other *.ts file of the app.

ng serve

Exception or Error

No response

Your Environment

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Angular CLI: 17.3.3
Node: 20.11.1
Package Manager: npm 10.2.4
OS: win32 x64

Angular: 17.3.3
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1703.3
@angular-devkit/build-angular   17.3.3
@angular-devkit/core            17.3.3
@angular-devkit/schematics      17.3.3
@schematics/angular             17.3.3
rxjs                            7.8.1
typescript                      5.4.4
zone.js                         0.14.4

Anything else relevant?

No response