Remove non-standard appearance keyword "slider-vertical"

Category: DOM
Type: Feature removal
Status: No active development (Chrome No active development)
Intent stage: None

Breaking change: Yes
Enterprise impact: None
Spec maturity: Unknown status
Web Platform Tests: Yes

WPT details: https://wpt.fyi/results/css/css-ui/appearance-cssom-001.html%3Finclude%3DInvalid?label=experimental&label=master&aligned

Summary

This is a continuation from feature RemoveNonStandardAppearanceValue (5066630972833792). Since only standard appearance keywords should be supported, we are removing the appearance (and -webkit-appearance) keyword "slider-vertical". Currently, many developers are using this value for <input type=range>, to allow the range element to go vertical. We shouldn't deprecate this value until the feature FormControlsVerticalWritingModeSupport (5602118873907200) is shipped.

Motivation

We should remove non-standard -webkit-appearance keywords and only support the keywords listed in the standards.

Standards & signals

Specification: https://drafts.csswg.org/css-ui-4/#appearance-switching
Firefox: Shipped/Shipping — Already deprecated. User can make input go vertical by using vertical writing mode or set orient=vertical (mozilla specific non-standard keyword).
Safari: Neutral — Currently still supporting the slider-vertical value, but agreed to deprecate.
Web developers: No signals

Ecosystem

Web Platform Tests: https://wpt.fyi/results/?q=css%2Fcss-ui%2Fappearance-cssom-001
Chrome Platform Showcase: https://chrome-platform-showcase.paulkinlan-ea.deno.net/features
GenDN reference: https://gendn.paulkinlan-ea.deno.net/features
chrome.dev demos search: https://www.google.com/search?q=site%3Achrome.dev+Remove%20non-standard%20appearance%20keyword%20%22slider-vertical%22
MDN Web Docs: https://developer.mozilla.org/en-US/search?q=Remove%20non-standard%20appearance%20keyword%20%22slider-vertical%22
Baseline status: https://webstatus.dev/?q=Remove%20non-standard%20appearance%20keyword%20%22slider-vertical%22

View on chromestatus.com