Migrate node-sass to dart-sass

[pedroferreira1]

Motivation

node-sass is not being supported anymore and we already had some problems trying to deploy the build with node v14 but it supports only until node v13. They are also suggesting to move to Dart sass

You can see the error (#144) and @r4mmer suggestion #144 (review)

Warning: LibSass and Node Sass are deprecated.
While they will continue to receive maintenance releases indefinitely, there are no plans to add additional features or compatibility with any new CSS or Sass features.
Projects that still use it should move onto Dart Sass.