Fix border spacing on multi-line comments

What does this MR do and why?

Even out the border, and lighten the color slightly to match regular border colors

before	after

How to set up and validate locally

1. Leave a multi-line diff comment
2. No more border

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Changelog:

Fix border spacing on multi-line comments

Changelog: fixed
EE: true