Fix layout issues with comments

Reported by @ivyreese:

both the parallax scrolling, and the comment text that i'm editing being pushed quite far down and to the right, are css mysteries that perhaps some motivated css ghost hunters will someday unravel

https://github.com/user-attachments/assets/32f4f733-0bdf-42a2-b404-5b8368261d93

when i type enough letters on the last line of a comment (like the "p" in this video), it changes how text earlier in the comment wraps.

https://github.com/user-attachments/assets/283aea21-bf61-4f16-8ed7-d02dbb0a803d

i can scroll way past the beginning and end of the comment

https://github.com/user-attachments/assets/c19a1e16-5358-484b-a361-e99ed1d66848

No files, tests, or entry points are named. Reproduce the comment-editing behavior from the attached videos, then inspect the CSS and layout around the comment editor. Done means parallax and positioning work correctly, text wrapping stays stable while typing, and scrolling does not extend beyond the comment.

Written by the indexing model from the issue text.