Bootstrap SCSS integration

[marcastel]

Cf. https://www.akashmittal.com/import-css-node_modules-svelte/
I would like alternate method (using svelte-preprocessor) to work.
Currently rollup.config.js is configured as per the first method

Important what triggered trying to change the method is that the generated CSS file is in the js/ directory instead of being located in the css/ directory. When trying to add relative/absolute paths for the CSS file, rollup bails out with an error saying that relative/absolute paths are not allowed!!!

Additionally the .map file for the generated CSS file is not produced.