BirdOne

BirdOne is a visual theme for the Thunderbird email program that changes how its window is laid out and colored. Its main idea is to combine the tab bar and the toolbar, which normally sit on two separate rows, into a single row, with tabs on the left and toolbar buttons on the right next to the window's minimize and close buttons. It also hides the built in global search bar, though a person can still bring it up with a keyboard shortcut. If the Thunderbird window gets narrower than 850 pixels, the theme automatically switches back to the normal two row layout so it still stays usable on small windows.

The theme also changes the color scheme in dark mode. Instead of using the operating system's accent color, it applies a fixed amber color to things like selection highlights, the main button, and focus outlines, so the look stays the same no matter what accent color is set in Windows. Hovering over menu items, toolbar icons, and other controls shows amber text or icons rather than a solid colored background, and selected items in the message list get a light amber tint with a thin amber outline instead of a solid block of color. Popup menus and panels use square corners instead of rounded ones, and several parts of the interface, including the folder list, message list, and reading pane, share one consistent dark grey background color.

To install it, a person downloads two CSS files from the repository, turns on a setting inside Thunderbird that allows custom stylesheets, places the files into a folder inside their Thunderbird profile, and restarts the program. The theme can be further adjusted through CSS variables, which are documented in a separate file in the repository. It only works with Thunderbird version 115 or newer, was tested on Windows, and a companion theme for Firefox with the same idea is linked from the README. The project is released under the MIT license.