Clear Linux window borders?

I gave Clear Linux a try but ran into something that doesn't work for me. I like having a solid black desktop and black background in my shell windows. However, the UI, as installed, has no visible window border. This doesn't work for black windows on a black desktop.

I searched for a way to tweak the UI to put a visible border around windows, but couldn't find anything. Is there a way to display a visible window border?

Thanks!