Darker theme has extra black bar in systray overlay

[jonathanjsimon]

Viewing a popup from the system tray contains this large black bar that isn't present on other themes. See attached screenshot. Not sure what other information is needed for this issue.

[KBeDevel]

Something similar happens when using the default Breeze dark theme

The weird part is this occurs only when I plug an external display.

I think this issue is more related to Plasma itself than any of the community themes.