[5.0] Fix undefined variables in scss

[Fedik]

Pull Request for Issue # .

Summary of Changes

Fix undefined variables in scss after

• [WIP][5.0] Dark Mode support #41409

Testing Instructions

run npm install

Actual result BEFORE applying this Pull Request

npm fail with error

Expected result AFTER applying this Pull Request

npm runs

Link to documentations

Please select:

• Documentation link for docs.joomla.org:
• No documentation changes for docs.joomla.org needed
• Pull Request link for manual.joomla.org:
• No documentation changes for manual.joomla.org needed

[richard67]

I have tested this item ✅ successfully on 8d668c5

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[Fedik]

I not very understood why it require extra import, but it seems helps.