Can't manage column border in mobile view

Hello everyone!
Adding or removing borders from columns, in this case in the footer, creates problems.
You can add them, but then you can't remove them!
I'm attaching a link to a video.
https://www.diamondsdance.it/varie/column_border.mp4
The website is at
www.diamondsdance.it
Many thanks to you all

Replies are visible only to logged in members with an active subscription.