This change does some initial work cleaning up the markup and CSS for the

entries on the review request page (review and change descriptions). The

changes involved are:

Removal of the use of the {% box %} template tag. This tag was adding a

  bunch of additional layers of elements, which weren't really helpful. We were

  overriding almost all the styles we got from them, and the very generic class

  names that it used meant that our CSS selectors were a lot deeper than it

  needed to be.
Updated class names within the entry headers to be a bit more sensible

  ("reviewer" -> "summary", "posted_time" -> "timestamp").
Removed the margin on the sides of the entries, making them the same overall

  width as the review request box (this wasn't too obvious before, but is much

  more after adding a new top-level item for the initial status updates which

  doesn't have the callout and avatar).
Tweaking of the spacing within boxes, especially collapsed ones, so that

  there's equal height on either side of the collapse button.
Fixed the color of the callout triangle for change descriptions to match the

  background of the box (it was previously white, which was so close that we

  didn't notice it before).

The details of the markup and class name changes have been added to

https://www.notion.so/Review-Request-page-changes-for-3-0-8d27aac9e3ed4f81ac1e849ebb6127fe

Created a review request with a handful of reviews and change descriptions.

Verified the appearance and functionality in both desktop and mobile mode.