How to use images in CSS code inside an Angular library

I've built a library that will be used by several Angular applications (multiple teams and no monorepo). This library includes a scss-theme. This theme uses two SVG-files. However, I can't get it to work. The path is always incorrect.

My theme scss:

.test::before {
    content: url('/test.svg');
}

I've written a Schematic that can be used by the library consumers to store the images inside a subdirectory of the assets folder of the application (e.g. src/assets/test-path). The Schematic does work as expected.

It does work when I add the following style inside the client's scss:

@import "test-company/test-lib/theme";

.a-client-test::before {
   // This is just an example and assumes that the test image is located at this path.
   background-image: url('../../assets/test-path/test.svg'); 
}

But as soon as I remove the line above (that actually uses the image from the assets folder and is not required at all). The path won't work anymore.

I've tested the following paths inside the library: ./test.svg, ~/test.svg, /test.svg. Only the latter does work but only with additional styles like the one above (that wouldn't be used) on app side. That's something I want to avoid as maybe we provide 50 icons on the library-side and it would be tedious to add these classes only to use the assets.

Some additional information:

1. I've added node_modules to the predecessor options in angular.json.
2. All other styles are working correctly. Only the image doesn't work.
3. I know that I can use ccsUrl: "inline" option inside the ng-package.json. However, I think this option only works (as far as I know) on styles that are used by components. But I actually copy the theme styles over after the build process. Additionally, the number of icons that are used inline shouldn't be too big, otherwise, the bundle size will increase and is therefore not an option for me.
4. I also don't know what is best practice for a scenario like that. I just couldn't figure out a proper way so far. But I assume writing a Schematic that copies over files is also not the best approach. Maybe there is a better way (e.g. a way to reference assets from the library but keep in mind I have the styles inside my library and the path is, therefore, complicated to figure out for all modules).

Just to make it clear again: My library has a scss file that uses an image. That image path is clear at the built time but doesn't work when used by an app. I can copy over the images, but that only helps when those images are used by the app somewhere in the styles. Then the path /image.svg works. The image as well as the scss that makes use of it are provided by my application.

Thanks for your help!