Re: [csswg-drafts] [css-scrollbars] Is the track visible in overlay scrollbars? (#9855)

My suggestion would be to add minimal normative text, and as well as informative text:

> If the user agent displays the scrollbar without the [=track=], they <em class=rfc2119>must</em> ensure reasonable contrast between the [=thumb=] and what is behind it.
> 
> Note: This is typically relevant in the case of [=overlay scrollbars=], either on platforms where the [=track=] is never displayed, or on platforms where it is only displayed when the scrollbar is being interacted with but not when scrolling with the mouse wheel or the track-pad. This does not apply in cases where the entire scrollbar is hidden as is often the case with [=overlay scrollbars=] while no scroll operation is ongoing <em>and</em> when the scrollbar is not being interacted with either.
> 
> Note: The user agent is free to achieve this by any of a variety of means, depending on the platform, on design choices, or on what is practical to implement, such as:
>  * Doing nothing if it can determine that contrast is already sufficient
>  * Doing nothing if the design and geometry of the thumb ensures that some part of it will always be visible regardless of what is behind it
>  * Adding an outline, shadow, or glow around the [=thumb=] to provide contrast (possibly using the [=track=] color as the contrasting color, or possibly using a different shade of the [=thumb=] color)
> * Adding some texture or geometry to the [=thumb=] so that it's color isn't uniform
>  * Drawing the [=track=] anyway in cases where not doing so yields insufficient contrast
>  * Replacing the [=thumb=] color with the [=track=] color when that provides better contrast
>  * Altering the luminosity of the specified [=thumb=] color while preserving its hue
>  * Disregarding the specified [=thumb=] color altogether and use automatically determined alternative

I think this needs to be a MUST because otherwise authors could pick colors that lead to unusable contrast through no fault of their own.

I think this can be a MUST because it is always possible to implement something that works.

It might be hard to implement given some design choices, but these are choices, and the user agent should be prepared to deal with the consequences of those choices. If the thumb isn't a single flat color with no geometry, no outline, and no shading, then this isn't an issue. If the track is shown whenever the thumb is shown, then this isn't an issue. Yes, user agents can chose to have a flat featureless thumb over no track, but that is what causes this issue, so that choice needs to come with countermeasures.

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Received on Thursday, 4 April 2024 02:10:21 UTC