Change Color in Testimonial Section

Hello, How can the color of the image elements on the "Testimonial" section be adjusted? See here: https://www.beautyofsilence.ch/?lang=en#testimonial-section I'm referring to the design element above the title of the testimonial. It's currently a white line and has a turquoise box in the middle of it. In particular the turquoise box needs a different color and it would be great to apply other designs to the white line too. Thanks for any insights. regards, Chris