Yay! It worked.
There was a custom folder for my template and the Gantry folks provided some guidance:
Gantry 5: Add Custom Style Sheet
Created an scss file in the custom folder as directed. Pasted the css Kyle provided here on this forum. Went to my Gantry template in the administrator and clicked on Recompile CSS.
Voila! The lines are gone from my member lists.
I'm adding this procedure to a file for myself so I can recreate if/when I change templates.
Thank you, Kyle! Again!