macOS 10.14 brings native dark mode. Not sure how this is integrated, but with a developer account for Apple, it should be possible to find out, how they are planning to deal with third party apps and which exact steps devs have to take to support this.
Steps to Reproduce:
macOS 10.14 dark mode but LO does not support it when switched to.
No dark mode on macOS.
Support for dark mode.
User Profile Reset: No
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Firefox/60.0
Interesting thoughts on dark mode from dev perspective:
As of 6.3, there also doesn't seem to be any simple way to even manually change UI items 'consistently' to any desired tone/background.
E.g., Preferences > Personalization > select the dark gray box: background of the menu bar changes, but nothing else (application background and side bar remain light). Manually changing App Colors > application background > dark grey fixes the app background but the sidebar remains light gray = eye sore :)
Just an FYI.
NeoOffice, a fork of LibreOffice which is Mac specific, and available in the App Store supports Mac dark theme.
Not only that but it also has multiple Mac specific improvements.
It is licensed under GPL3 as LO, so maybe we could bring their code to mainline LO.
*** Bug 130714 has been marked as a duplicate of this bug. ***