Reduce header and footer height of comments

What does this MR do and why?

Reduce header and footer height of comments, header to 40px, footer to 32px

Screenshots or screen recordings

Before	After

How to set up and validate locally

Open any issuable that accepts comments (issue, merge request, epic...) and check the header and footer of the comment form.

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.

Related to #363289 (closed)