Header in URL widget occasionally doesn't appear on hover.

Steps to reproduce:

1. Create dashboard and add URL widget
2. Fill in the fields:
   • URL field: ssh://zabbix.com
   • Show header: unselected
3. Save widget and dashboard
4. Move mouse from the bottom toward the widget (see video)

Result:
Header sometimes doesn't appear on hover

Expected:
Widget header is visible on mouse hover