Formatting byline like footer
 

I would like to have the date of the post in the byline instead of the footer, and I learned how to do it, but I would also like the format to be the same as the footer (a grey box). By default, byline appears as a normal text on the white background that is not distinguishable from the text of the main post. How can I edit the format?
P.S. I just started working with Atahualpa and want to say that I love it. Thank you for your amazing product!

What version of atahualpa and wp?
What is the URL showing the issue?
How did you add the dat?