[csswg-drafts] [css-ui] Auto-disable native appearance when cascaded value has author origin (#4777)

andruud has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-ui] Auto-disable native appearance when cascaded value has author origin ==
Browsers currently automatically disable the native appearance of widgets in some cases, even if 
`appearance` is e.g. `auto` (see [issue 11](https://drafts.csswg.org/css-ui-4/#index)). This can happen when the author styles the `border`, `background`, or in Firefox's case `padding` (I believe).

This issue is not about _which_ properties disable the native appearance, but _how_ they disable appearance, which is quite different in Firefox (which has reasonable behavior) vs Chrome/Safari (which has ... less reasonable behavior):

In Chrome (and as far as I can see in Safari), the native appearance is disabled when the author styles the background/border in such a way that it differs from the _would-be_ background/border had only UA-origin declarations existed. This approach isn't great, because:

- Tweaking the UA-style due to e.g. a redesign of widgets can toggle native behavior on or off in the wild. (This exact thing happened in Chrome recently).
- You can get different results in multiple dimensions: for each type of widget, each OS, each browser, depending on what's specified in the UA sheets. This also makes it entirely incomprehensible for authors. 
- It adds annoying technical complexity, since we must somehow know the computed values of an alternate cascade-reality that shouldn't need to exist.

Instead, we should specify that border/background/etc applied by the author origin disables the native appearance _regardless of their value_. This is (to the best of my knowledge) what Firefox does currently.

See also related [Intent to Ship on blink-dev](https://groups.google.com/a/chromium.org/forum/?authuser=0#!topic/blink-dev/uNKeyd8091A).

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4777 using your GitHub account

Received on Friday, 14 February 2020 08:06:14 UTC