Resizable text fields need limits

I have some simple recommendations. I could not figure out how development works using git and zites, so I'll just lay it out here.

I believe it looks strange for the `comment_body` and `topic_body` elements to be able to be horizontally resized. It would make sense to set `resize: vertical`. The `topic_body` element is especially messed up on horizontal resize.

It also makes sense to me to set the minimum height of the `textarea`s to the height of a line (24px) plus the paddings (20px) and borders (4px) = 48px, which looks like this:

`comment_body`:

`topic_body`:

Thanks.