I have trouble seeing the markings to the left and right of a paragraph: the flippy triangle (I don’t know its formal name), the vertical lines from one flippy triangle to another (I don’t know its formal name either), and the focus arrow.
I was able to make my own Theme where the focus arrow is black, and this works. But I have not found anything that I can make black in the theme that will make the flippy triangle and vertical lines black (or any other color). I tried setting the handle and guideLine colors, in the hope that these might the ones, but no matter what I do, the flippy triangle and vertical lines are a faded gray.