This thunderbird theme is meant for dark themes
and complements my 4CLIX-Nuvora theme.
Created new chrome folder including userChrome.css, "tweaks" and "themes" folders
It is a revision of the monterail theme
Thanks to Sagnik Anupam, Matthew Richardson, https://monterail.com, et all

Installation instructions:
Delete previous chrome folder (if it exists)
Add chrome folder to the present default profile (it is the one that has today's date)

Menu > Density = default (choose the one in the middle)

Menu > Settings > General > Config Editor... (at very bottom right)
Enter in search window:
toolkit.legacyUserProfileCustomizations.stylesheets
Toggle from: "false" to: "true"