css: refactor CSS to use Tailwind-style utility classes.

Refactor CSS to use standard Tailwind-style utility classes instead of
ad-hoc rules. This eliminates a lot of single-purpose rules for specific
UI elements and standardizes margins to be more consistent throughout
the site.

Utility classes are defined manually on an as-needed basis instead of
importing Tailwind as a whole. Naming conventions mostly follow
Tailwind's conventions, otherwise they follow Bootstrap.

* https://tailwindcss.com/docs/
* https://getbootstrap.com/docs/5.0/utilities/spacing/

app/javascript/src/styles/specific/wiki_page_versions.scss

@@ -10,10 +10,4 @@ div#c-wiki-page-versions {
       text-decoration: none;
     }
   }
-
-  #a-index {
-    table {
-      margin-bottom: 1em;
-    }
-  }
 }