VLC seems to use Qt5 theming, whereas Adwaita-Dark is a gtk theme. These are different GUI toolkits. They use different code to draw things like buttons and menus etc. Linux programs do not universally share one windowing toolkit, and thus do not all share one global theme setting.
QT5 allows importing GTK themes like Adwaita-Dark. To enable this, i had to install qt5ct (qt5 change theme) and required dependencies, then ensure that
was set in my environment.
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This can be set globally by adding QT_QPA_PLATFORMTHEME=qt5ct
to the file /etc/environment, and restarting X.
.
You can also set it temporarily within a shell session with "export T_QPA_PLATFORMTHEME=qt5ct" in your current shell.
Then you can start qt5ct and select gtk2 as your style
.
Hit 'Apply' and 'Ok', then after restarting vlc, you should get Adwaita-Dark for your colors.
.
While this is not necessarily a 'VLC problem', it is a problem many will encounter, so it would be very helpful if VLC could ease this process, or at least point to a brief explanation of the issues with GTK and QT theming similar to what I have posted here.
Thanks!