Re: [csswg-drafts] [css-borders] Add a 'hairline' border-width value (#3720)

The use case is not actually "render a border 1 device pixel wide". If you have a thoeretical future screen with 100dppx, you don't want the border that small - it would be practically invisible. The use-case is "render a border thinner than 1px, if it's possible for the screen to do so while maintaining the sharp line we expect from borders". You can do lines that thin in print, and it's totally reasonable for many cases. So providing a `dp` unit would just mean that, in a future where screens that high-res exist, we'd have to redefine `dp` to be a "virtual device pixel"`, like we do with `px` today, and keep it from getting too small, or else sites would end up with effectively invisible UI that the author did not originally intend.

> Is the idea that [drafts.csswg.org/css-values-4#snap-a-length-as-a-border-width](https://drafts.csswg.org/css-values-4/#snap-a-length-as-a-border-width) will then ensure that non-zero border widths are at least 1 hairline instead of the current 1 device pixel? For values above that, will the rounding be to an integer number of hairlines or still device pixels?

Min of hairline, increments of device pixels.  (There's no guarantee that a hairline width will evenly divide 1px - on a 5dppx screen, a hairline of 2dp might be reasonable, for instance.)

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Received on Wednesday, 21 May 2025 18:48:38 UTC