Subscription Block: Border color in the editor isn't consistently reflected properly in preview or live

### Impacted plugin

Jetpack

### Steps to Reproduce

Testing with the 10.7 Beta, add a Subscription block (after enabling subscriptions in Jetpack > Settings> Sharing) and add a border of any width and color.

### A clear and concise description of what you expected to happen.

The border color as visible in the editor is the same as the border color in the live preview, and published post.

### What actually happened

Trying with several themes, in some cases the border color will differ in the editor and live, depending on the color and theme (an example being the Twenty Twenty theme with #6d6d6d as the border color).

### Other information
First reported here: p8oabR-Oy-p2#comment-6030

In the editor:

Live:

### Operating System

macOS

### OS Version

12.1

### Browser

Chrome/Chromium, Firefox

### Browser Version(s)

_No response_

Reproduce the Subscription block with subscriptions enabled, testing border colors in the editor and live view across several themes, especially Twenty Twenty with #6d6d6d. Compare the two renderings and confirm the work is done when the configured border color matches in the editor, preview, and published post.

Written by the indexing model from the issue text.