Comment form for an article on mobile is not displaying correctly

Hello,
First, what a work on this version 6! Impressive.

Concerning the subject. On tiny the labels are displayed on 2 lines and the warning is half hidden under the textarea.
Screenshot
Is it possible to replace labels with placeholders to keep the page as short as possible or at least place them above and which class or id to add a margin to clear the warning please?

Another small thing, the comment form and the share buttons are both intended to be displayed at the end of one article but their titles do not have the same font size. H3 to Leave a comment and H5 to Share this post.
Screenshot
I will correct with CSS but it would perhaps be good to harmonize.
Thanks for your attention.