openstyles/stylus
Stylus
Stylus is a browser extension for installing, managing, and editing user-created CSS themes that customize the appearance of websites. It provides a central interface for organizing, enabling, disabling, and removing installed styles, and includes a built-in CSS editor with syntax highlighting and linting support.
The extension supports the UserCSS format, allowing users to install themes from .user.css files or URLs, and generates a basic UserCSS template with required metadata fields when creating new styles. Stylus can watch local .user.css files for changes and automatically apply edits to matching web pages without manual refresh, and it checks for and applies updates to installed styles using configurable per-style and global update settings.
Stylus enables users to customize style properties at install time through a dynamic dialog generated from @var definitions, and provides backup and restoration of style collections as JSON files compatible with other userstyle managers. The extension also supports cross-device synchronization of installed styles through cloud storage services like Dropbox, Google Drive, or WebDAV.