CiviCRM 5.6.0 Joomla 3.8.12 php 7.0.32
On the activities tab of a contact, when you create or view an activity, the panel which pops up is displayed behind the black CiviCRM menu bar, and also behind the main Joomla menu bar. The same happens with when you view an activity in the Find Activities results page.
Not a big deal, but needs fixing.
Update: it's not only the activities page/tab. It seems to be every page. Wherever there's a pop-up window or a pull-down menu, the black CiviCRM menu is in front of it.