Changing the color of the diagonal borders in the “Creative Studio” demo

Using the “Creative Studio Demo” the borders are diagonal lines. I would like to change the color of those lines so they can stand out more (company colors). Please note that the color does not match either the top or bottom sections. It was done once before (if memory servers it was done with CSS code) but lost the information due to a HD crash and I cannot remember what I had done.

Thanks for any and all help.