You can add another includePaths to your render options.

Plain example

Snippet based on example from Oncle Tom.

var options = {
  file: './sample.scss',
  includePaths: [
    path.join(__dirname, 'bower_components'), // bower
    path.join(__dirname, 'node_modules') // npm
  ]
};

sass.render(options, function(err, result){
  console.log(result.css.toString());
});

That should do. You can include the files from package using @import "my-cool-package/super-grid

Webpack and scss-loader example

{
  test: /\.scss$/, 
  loader: 'style!css!autoprefixer?browsers=last 2 version!sass?outputStyle=expanded&sourceMap=true&sourceMapContents=true&includePaths[]=./node_modules' 
},

Notice the last argument, includePaths has to be array. Keep in mind to use right format

You can include node_modules in sass pathes:

.pipe(sass({
  includePaths: ['node_modules']
})

Then you can import library's sass like this:

@import "bootstrap/scss/bootstrap";

Or, in case of material-components-web:

@import "@material/top-app-bar/mdc-top-app-bar";

This way:

• you don't need to add each lib to path
• the sub-dependencies imports will work seamlessly, e.g. mdc-top-app-bar in MDC example imports "@material/elevation/mixins".

As per latest angular 18, I faced same problem, I fixed it by simply removing the ~ symbol

Code which shows error

@import '@angular/material/prebuilt-themes/indigo-pink.css';
@import '~bootstrap/dist/css/bootstrap.min.css';
@import '~perfect-scrollbar/css/perfect-scrollbar.css';

What is the error

[1] Could not resolve "~bootstrap/dist/css/bootstrap.min.css"

What info given after the error

[1] You can mark the path "~bootstrap/dist/css/bootstrap.min.css" as external to exclude it from the bundle, which will remove this error and leave the unresolved path in the bundle.

Fixed code

@import '@angular/material/prebuilt-themes/indigo-pink.css';
@import 'bootstrap/dist/css/bootstrap.min.css';
@import 'perfect-scrollbar/css/perfect-scrollbar.css';

Regarding ngx-toastr/toastr.css it does not declare files in that package.json, this cannot be imported in your css or scss, therefore it should be imported via angular.json

"styles": [
   "src/styles.scss",
   "node_modules/ngx-toastr/toastr.css"
]