I think the main difference between the two are the way API are served. Some smelte components need you to input big chunk of json as props, while i prefer keep props as primitive types and in the other hand give you different components tags to compose.

Before showing the final result of the .svelte components we will also add Material-UI, using the adapted version.

After a few hours experimenting (updated NPM, NODE, ...) I found that renaming _smui-theme.scss to smui-theme.scss (without underscore prefix) solved the problem. I don't understand the mechanics behind (why in documentation is file with prefix).