It does not alway work
I wrote a CSS class zeroborder in /admin/config/development/css-injector/edit/22:
td.zeroborder
But no joy. Tried it on this other page, in the right-hand side block. I used a two-column layout instead of a single table with four columns to be friendlier to small screens: Edgeryders had about 1K visits from mobile last month, with the iPhone being the most popular mobile device with 316 visits.