Change line at end of my posts

Hi,

I need help with the following problem:

At the end of my blogposts there is a double black line showing, a thin line with a thicker line under it.
I would like to change this to a single line in a different colour or a dotted line or something like that

I can see this code
background: url(‘images/break.gif’) repeat-x bottom center;

So I guess i have to adjust something that has to do with images? But don’t know what…

My site:
https://pinktaste.nl/

Thanx!