Migrate to plain CSS (remove CSS modules) (#659)

* Migrate to plain CSS (remove CSS modules)

Change `prefixer` to a function instead of a proxy

* Switch prefix to `nc`

* Replace prefixer with literal class names

* Remove prefixer

* Fix migration errors

* fix compose migrations

* Remove unnecessary theme imports

* Remove old CSS import

* fix sticky toolbar positioning

* update to cssnano v4 so preset is used

* fix css pseudo selectors

* update lockfile

postcss.config.js

@@ -12,5 +12,8 @@ module.exports = {
         },
       },
     }),
+    require('cssnano')({
+      preset: 'default',
+    }),
   ],
 };