Reorganize various CSS files for clarity, group together by subdirectory in `index.css`. This reorders some of the rules, but I don't think it should introduce any issues because of that.
Since 2015/2016, there is a global pollution: ".ui.left" / ".ui.right". Fomantic UI doesn't work this way, it just conflicts with many Fomantic definitions. This PR starts the cleaning work of such techinical debts. And, the "label list" page has been quite messy for long time, for example, why "li" appears in "div" ...... And fix #24296 <details> ![image](https://user-images.githubusercontent.com/2114189/235051281-54c5374c-b5fd-4b5f-9aa2-02d4bb2d9112.png) ![image](https://user-images.githubusercontent.com/2114189/235055703-2ba042e0-4db7-4e63-8646-02f390d496b5.png) ![image](https://user-images.githubusercontent.com/2114189/235056310-4f6ffdc2-5758-4927-8fb8-314d9fb72a6b.png) ![image](https://user-images.githubusercontent.com/2114189/235058400-dab1c9ec-3325-4671-8345-aee6b0b68042.png) ![image](https://user-images.githubusercontent.com/2114189/235058424-85509532-b9bc-43ad-b00f-a87184c60f22.png) </details>