All of the Admin section is pretty usable on mobile except for the Permalinks page at admin/customize/permalinks. It shouldn’t be very difficult to see how the existing CSS works for the other admin/customize/ pages and make this page responsive.
Sounds like a fun #starter-task for someone who’s learning CSS!
Whenever possible, we definitely prefer to keep the desktop and mobile styles separate. It’s a lot more organized to have all related styles in one place.
So, try to have a look at making the changes in the mobile stylesheet if possible.
