I'm trying to write a post with
Think of markdown as a nicer syntax for HTML – it's only the content, no styling. (Centering would be styling.) You cannot center text in HTML either. But you can add classes, then style them with CSS (in your Hakyll theme).
Pandoc markdown currently supports attributes on images:
but not paragraphs, however you can wrap stuff in
# my markdown header <div class="myClass"> one paragraph second paragraph, **strong** </div>