styling default hr tag

I have restyled my default hr tag, and would like to also apply my customized style to the horizontal line that Atahualpa automatically inserts at the end of pages and posts. For example, on this page: http://mihansa.net/also-with-yun-jung-hun I'd like the horizontal line above the Share this: buttons which was inserted automatically by the theme to match the two horizontal lines I inserted manually above the two h5 headings.

I have not been able to find the styling for this line. I know a little html, but no php, and it doesn't seem to be in the obvious files (style.css, css.php).

Can anyone help me identify the element, and compose the code I need to use to style it (hopefully I can do this in html/css inserts)?

Many thanks in advance!