chore: limit portal root vars to portal

[wesleyboar]

Overview

Limit Portal variables defined in :root from affecting CMS.

The `tup-cms-react` app loads Portal's `imports-….css` globally, so any `:root` rules inside it have affect on CMS. This is a no-op, because CMS is not using any of these variables, but it could. And their values should not be influenced by what is just for Portal.

Related

• noticed during #321

Changes

• changed tup-ui usage of :root to #page-portal

Testing & UI

N/A.