node-sass is deprecated [#3588350]

node-sass is deprecated and no longer maintained. The maintainers are recommending sass instead.

Remove node-sass from package.json and replace with sass. Because of this we can't use node-sass-magic-importer so imports will need to be explicit.
The darken and lighten SASS functions are also deprecated and should be replaced with color.adjust.
Use sass-migrator module --migrate-deps to fix the import deprecations as described here.
Correct comments to be more Sass-style and spacing at the bottom of files.

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3588350-node-sass-is-deprecated changes, plain diff MR !81
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