Dark theme forked from maujin111's "than dark theme" for libresprite (see https://github.com/maujin111/than_dark_theme_libresprite) and made to fit color pallete from Adapta Nokto Gtk+ Theme for Linux (https://github.com/adapta-project/adapta-gtk-theme)
Open LibreSprite.
Go to Edit/Preferences/Theme, you can see there are 2 paths at the top of the Available Themes list.
For example on windows:
-- C:\Users<your-username>\AppData\Roaming\Libresprite\data\skins\ --
-- C:\Program Files\Libresprite\data\skins\ --
or linux:
-- /home//.config/libresprite/data/skins/ --
-- /tmp/.mount_LibreShxiPnk/usr/bin/data/skins/ -- (You should need be root user to modify this directory)
Choose 1 of them then click Open Folder. Copy the file you've just downloaded here and extract it.
Open the Preferences/Theme dialog again, choose a theme from the list, click Select then click OK. Restart Libresprite to make the change happen.