According to developer and blogger Jane Manchun Wong, it appears that LinkedIn is working on adding a dark mode. Jane made this observation in LinkedIn's mobile app for android by looking into the code underneath. However, LinkedIn has not officially released the Dark Mode.
The dark or night mode is a software feature that makes the user interface darker. It transforms bright backgrounds to a dark colour and changes text from dark to light. This results is a form of inverted interface that has mostly dark colors.
The dark mode is particularly of interest to developers and other users who stare at the screen for a very long time since the background produces less eye strain.