I feel like maybe you don't know what a headless component library is. A cli has a head -- the terminal. Headless applications, by definition, have no visual portion. For instance, a headless browser is a browser where the web page renders in-memory, but never displays any content. A headless component library, then, is one where the implementor doesn't provide anything visual, only behavior. For web dev, is very helpful -- the library implementator writes all the js, but the css and html (the "head") are left to the user for use. The best headless component libraries, then have nothing to screenshot without the user supplying some implementation.