Add image border in Markdown preview
What does this MR do?
- add image border in Markdown preview like it is show after a comment is saved
- fix margin and shade of
<hr>in Markdown preview
Are there points in the code the reviewer needs to double check?
.md the right class to use?
Why was this MR needed?
The border was missing.
What are the relevant issue numbers?
fixes #19652 (closed)