Feat: add non-highlighted attribute

Attribute can be used for example to style non-dragged (so non-highlighted) slots during drag and drop. Videos: https://github.com/user-attachments/assets/b2e5021f-a7b0-4608-8261-700967b752d6 https://github.com/user-attachments/assets/6e95abb4-c550-40b2-9e68-be0a5b25a8ca