Here is a screenshot with a painted line, as thin as I could make it, showing the approximate placement of the hairline. I simulated the hairline because it does not show in any screenshot. Please notice how it passes through the title of the window and terminates near the bottom of the screen. The hairline, unimaginably thinner than the line I painted over the screenshot, stays fixed where I indicated, independent of all screen content.
It is either a Linux Maté coding fail, or perhaps an issue with my graphics card. How do I troubleshoot this?
Thank you for considering my request,
Bob