FluentBird: A Windows 11 Fluent Design Theme for Thunderbird

FluentBird is a userChrome.css theme for Mozilla Thunderbird, bringing the sleek Windows 11 Fluent Design and Mica transparency to your inbox. Supporting both light and dark modes, it enhances Mica transparency on Windows 11 systems. While a beta release with potential bugs, it largely themes the mail section and fixes several issues. Installation involves manually placing files in Thunderbird's chrome directory. Note: some Thunderbird areas use Shadow DOM, limiting complete theming; the new message window and settings remain untouched.