demo-env-specific-config-build-angular.json

"configurations": {
  "production": {
    "fileReplacements": [
      {
        "replace": "src/environments/environment.ts",
        "with": "src/environments/environment.prod.ts"
      }
    ]
  },
  "development": {
    "fileReplacements": [
      {
        "replace": "src/environments/environment.ts",
        "with": "src/environments/environment.dev.ts"
      }
    ]
  },
  "local": {
  }
}

demo-env-specific-config-serve-angular.json

"serve": {
  "builder": "@angular-devkit/build-angular:dev-server",
  "configurations": {
    "production": {
      "browserTarget": "demo-angular-env-config:build:production"
    },
    "development": {
      "browserTarget": "demo-angular-env-config:build:development"
    },
    "local": {
      "browserTarget": "demo-angular-env-config:build:local"
    }
  },
  "defaultConfiguration": "local"
}