🛠 Tooling: Remove as much as possible from index.css files

[JoshuaKGoldberg]

Tooling Report Checklist

• [X] I have tried restarting my IDE and the issue persists.
• [X] I have pulled the latest main branch of the repository.
• [X] I have searched for related issues and found none that matched my issue.

Overview

index.css files should be exclusively styling the UI around games+buttons+menus. They shouldn't be used to style games, buttons, or menus themselves.

Are there any styles in index.css files that still apply to games?

Additional Info

No response