Trac has some unusual or better said special conventions about default URL paths (or URL endpoints). These are specified relative to base Trac URL.

• /chrome - the handler for this URL just serves files that are placed in htdocs folder of Trac environment.

These files are usually images, CSS and .js that are called static resources, because they won't require any server-side processing. In fact to avoid firing Trac request handling many prefer setup when static resources are served by web server directly.