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 Desktop Packages, which is subscribed to gnome-calendar in Ubuntu. https://bugs.launchpad.net/bugs/1552908 Title: gnome-calendar is not compatible with gnome dark theme Status in GNOME Calendar: Unknown Status in gnome-calendar package in Ubuntu: Fix Released Bug description: Hello, if I activate gnome global dark theme, all the gnome apps theme are dark, but not gnome calendar... Thank you for your help. LGDN ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: gnome-calendar 3.19.91-0ubuntu1 ProcVersionSignature: Ubuntu 4.4.0-9.24-generic 4.4.3 Uname: Linux 4.4.0-9-generic x86_64 NonfreeKernelModules: nvidia_uvm nvidia ApportVersion: 2.20-0ubuntu3 Architecture: amd64 CurrentDesktop: GNOME Date: Thu Mar 3 21:52:56 2016 InstallationDate: Installed on 2012-07-07 (1335 days ago) InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425) SourcePackage: gnome-calendar UpgradeStatus: Upgraded to xenial on 2016-01-31 (32 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-calendar/+bug/1552908/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp