This is fixed in Ubuntu 17.04 Alpha. dark theme support was explicitly disabled until GNOME 3.22 because it needed improvements to GTK, gnome-calendar and the Adwaita theme. I don't believe this is fixable in Ubuntu 16.04 LTS.
** Changed in: gnome-calendar (Ubuntu) Status: Incomplete => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1552908 Title: gnome-calendar is not compatible with gnome dark theme To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-calendar/+bug/1552908/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs