Whiter Than White: A CSS Quirk That Pushes Past Display Limits
Dongsung Kim has surfaced a strange CSS behavior that can push on-screen whites beyond what users have set their displays to. The demo relies on hidden HDR videos running at the corners of the page; when an HDR-capable browser detects one, it flips into HDR mode.
From there, the trick hinges on an unusual interaction. Kim reports that pairing backdrop-filter with a brightness value above 100% seems to behave like HDR, hitting the panel's maximum HDR brightness rather than the user-controlled level—and everything between follows along. He freely admits he's not sure why the combination works, only that it does.
Browser-By-Browser Results
The effect is inconsistent across engines. In Chrome, the demo shows an extra-bright text-shadow; Safari renders extra-white text. Firefox, meanwhile, matches the whites so closely that nothing looks unusual—a sign this is likely a rendering bug rather than a supported feature.
Why Not To Use It
Kim's own advice is to avoid this approach: the extra whiteness probably drains battery even when video isn't actively playing, since it's pushing hardware beyond what the user has requested. The silver lining, he notes, is that the broader web color gamut is expanding, so accessible brighter whites may eventually arrive through more conventional means.
