Refinement for the New Feature Announcement area

[Vinnl]

This PR fixes a couple of issues identified in #1561. Specifically:

You'll want to add an extra rule to remove this for the last item.

#1561 (comment)

Done in c9a159c.

I can't seem to close the tab when clicking the news button again.

#1561 (review)

Done in a967d58.

Kooha-03-01-2022-14-32-10.mp4

It also fixes #1583.

As for

Another thing is that when I shrink the device width, the panel gets cut off at a certain breakpoint (around 762px). Are we keeping the whats new feature on mobile as well?

Since it switches to a drop-down menu on mobile, I decided to just not show it there for now, since that interaction (a drop-down in a drop-down) can get very gnarly very quickly. It's there in #1562, though that might at some point need to transition to a drop-down as well.

How to test:

• l10n dependencies have been merged, if any.
• I've added a unit test to test for potential regressions of this bug (or this is a front-end change, where we don't yet have unit test infrastructure).
• I've added or updated relevant docs in the docs/ directory.
• All UI revisions follow the coding standards, and use Protocol tokens where applicable (see /static/scss/libs/protocol/css/includes/tokens/dist/index.scss).
• Commits in this PR are minimal and have descriptive commit messages.

[Vinnl]

Added 8ad30eb to fix #1583 as well.

[codemist]

LGTM - Wondering if we should make it closeable by clicking outside of the panel too.

[Vinnl]

@codemist That is already the case! (That's what window.addEventListener("click", close); does - it adds an event listener for clicking anywhere in the window.)