Calibre Dark Theme About View Calibre documents in a dark mode theme Using RES dark-mode color scheme CSS is clean Install Copy contents of CSS file Open an ebook or document On the (left side) menu open Preferences In Preferences > Userstyle paste contents of CSS file, click OK In Preferences > Theming click Save Resources Project is based off of: https://github.com/lorenrogers/calibre-themes