The popup currently has a fixed size based on monitor size. As a result,
the popup's content may overflow if its minimum size is larger than the
popup size. To prevent this, use min-width/min-height for the popup size
so that the popup can grow if necessary.
https://bugzilla.gnome.org/show_bug.cgi?id=696523
Implement a basic OSD popup that shows an icon and optionally a label
and a fill level. It is based on the existing OSD implementation in
gnome-settings-daemon, which it will replace.
https://bugzilla.gnome.org/show_bug.cgi?id=613543
