Change color of dashed line between testimonials

I would like to change the color of the dashed line between testimonials in a testimonial section. I have the testimonial settings set to Testimonial Grid and 1 column. I was able to change the color using a “line-specific” CSS (in other words, that would change the color of just one line), and I could replicate that for each line, but I want to set a general CSS so that the client can add testimonials and neither he nor we have to go in and add more CSS. The line I am referring to is the bottom border of each testimonial.