prefers-color-scheme · reduced motion · forced colors · contrast · pointer type · 20+ media queries → stable device fingerprint · no permission · runs locally
css prefers-* media queries expose your accessibility and display preferences to any webpage — with no permission, no api call, and no user interaction. dark mode, reduced motion, forced colors, pointer type, hdr capability, data saver, and more. the exact combination of matched queries is a stable fingerprint of your os configuration and hardware.
it updates live as you change system settings.
matchMedia call resolves synchronously and silently. there is no api that blocks or notifies the user. the entire preference profile is readable before the page finishes loading.forced-colors: active is almost certainly on windows with a visual impairment.prefers-reduced-motion: reduce often indicates vestibular disorders or epilepsy risk. this data is medically sensitive.color-gamut: rec2020 narrows you to premium oled displays. dynamic-range: high confirms hdr hardware. combined with screen dpr and dimensions, this identifies your device model class with high confidence.