Not ‘CSS-only’

Works fine with JS, but is not ‘CSS-only’—without JS, your page stays blank (like with most loader animations). IMO ‘CSS-only’ does not only refer to absence of images, so should work with only CSS. If you want to use JS events, you could use a CSS-only fallback and only inject the JS-dependent loader using JS itself—usable page for everyone and would truly work with ‘only CSS’ (though still not truly ‘CSS-only’).