Atahualpa, how to edit line above posts

Hi,
(This is driving round the bend!)
In the atahualpa template, on the page that displays a post on its own, before the post container, at the very top of the centre colum Atahualpa includes a line across the top about 4 px wide.
I want to edit this line, delete or change its colour to make it disapear in the background.
But I cannot fin where it is!

Similar ones apearing on multiple post pages dissapeared whe I got rid of the content above and below the loop. But I can’t find that one.

It is not the line at the beguining of the post container.

I leave a link to a page with the line right at the top, white over the dark background.

https://wadhurstbrassband.co.uk/wadbrass/wp/index.php/2010/12/hello/

Thanks a lot