Disable popover on mobile not working

I've tried several pieces of code from this forum to try to make it so the popover is not showing on the mobile site, but none of them has worked.

They were basically all variations of this going into the CSS.

@media all and (max-width: 728px) {
  div.visiblebox {
    display: none;

Anyway, it's still there on the mobile site regardless.

The site is http://westgatelaw.com