UI: For all changes to the "outer UI", like (status bar, file navigation etc.), take a look at the Theme Color reference.
Syntax: For changes to the "code highlighting", examine the syntax scopes by invoking the Developer: Inspect Editor Tokens and Scopes command from the Command Palette (Ctrl+Shift+P or Cmd+Shift+P on Mac) in the Extension Development Host window.
Icons: For changes to the icons, take a look at the File Icon Theme reference.
Commit your changes and open a PR.
Note:
Changes to the theme files are automatically applied to the Extension Development Host window, so no reloading should be necessary.
Publish
Squash and merge Pull Requests that are ready to be published into main.
Login as a publisher: npm run login
Run npm run package -- [version]. Follow the SemVer convention and replace [version] with one of the following options:
patch for bug fixes
minor for improvements
major for breaking or bigger changes
Push your changes to GitHub
Run npm run release to publish the theme on the Marketplace.
Credits
This theme was inspired by the official Windows 98 / Windows 2000 / Windows NT themes. The Code Editor theme scheme was inspired by the default Light (Visual Studio) theme shipped by VS Code. File icons are credited to Alex Meub.