Add CSS rules for basic colored labels (#23774)
Before:
<img width="164" alt="Screenshot 2023-03-28 at 23 35 46"
src="https://user-images.githubusercontent.com/115237/228372437-663111b9-7285-4fa2-9125-fb5e1cad21d7.png">
After:
<img width="166" alt="Screenshot 2023-03-28 at 23 35 54"
src="https://user-images.githubusercontent.com/115237/228372441-49430517-6b2d-4389-b11c-c30a724f6de7.png">
Also I removed the `!important` on the primary label as it's very likely
unnecessary with the amount of specificity the selector already has.
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