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fix(ui-theme): gate the standard scrollbar properties behind the missing WebKit pseudo-element

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A non-`auto` `scrollbar-width` or `scrollbar-color` makes Chromium and Safari
discard every `::-webkit-scrollbar*` rule for that element, including
`::-webkit-scrollbar-thumb:hover`. Declaring both unconditionally left the
hover tokens rendering nowhere: the engines implementing the hover
pseudo-element are exactly the ones the standard properties silence, and
Firefox has no hover pseudo-element to fall back on. Both hover tokens and all
four elevated surfaces' hover rebinds were therefore dead code.

Measured in chromium on probe elements with `scrollbar-gutter: stable`: an 8px
`::-webkit-scrollbar` alone reserved a 30px band, and adding
`scrollbar-width: thin` dropped it to the 10px `thin` reserves.

The standard properties now sit inside `@supports not
selector(::-webkit-scrollbar)`, so Firefox takes them and WebKit-based engines
take the pseudo-elements. The WebKit rules stay ungated: an engine without
those pseudo-elements drops them as unknown selectors, and gating them would
hide them from an engine that implements them without `selector()` — the
pre-16.4 Safari the ungated form serves correctly.

Three unit assertions pin the split by source offset, which the existing
at-rule-flattening parser cannot see. The web e2e now reads the path chromium
actually takes: the `auto` standard properties as the gate's signature, the
pseudo-element sizing and track, the indirection variables resolved per
throwaway probe, and the hover declaration as cascade rule text — chromium
folds the `:hover` rule into `getComputedStyle(el,
'::-webkit-scrollbar-thumb')`, so no computed query separates the states.
This commit is contained in:
Chinesezjc
2026-07-28 15:02:20 +08:00
parent a6b0cd6f8d
commit c3e9690b2e
9 changed files with 251 additions and 80 deletions
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4
packages/client/ui-theme/README.zh.md
View File

@@ -6,7 +6,9 @@
`src/styles/` 下有五张样式表，全部由 web 壳的 `base.css` 导入：`base.css`、`design-platform.css`、`scrollbar.css`、`gradient-shadow-text.css` 与 `shiki.css`。`scrollbar.css` 是 `--dsw-alias-scrollbar-*` token 的唯一消费方，必须排在声明这些 token 的 `design-platform.css` 之后。
滚动条重新绑定契约：`scrollbar.css` 在 `body` 上把 `--dsh-scrollbar-thumb` 与 `--dsh-scrollbar-thumb-hover` 绑定到 l1（基础表面）token，标准属性 `scrollbar-color` 与 `::-webkit-scrollbar-thumb` 规则都读取这一组变量。抬升表面（菜单、浮层、对话框）在自己的容器上设置 `--dsh-scrollbar-thumb: var(--dsw-alias-scrollbar-bg-l2)` 与 `--dsh-scrollbar-thumb-hover: var(--dsw-alias-scrollbar-hover-l2)`；一次重新绑定即可为两种渲染同时换色。推理过程与实测计算值见[滚动条 Agent Note](../../../.agents/notes/implemented/bug-fix/2026-07-28-themed-scrollbars-and-reserved-gutter.md)。
滚动条重新绑定契约：`scrollbar.css` 在 `body` 上把 `--dsh-scrollbar-thumb` 与 `--dsh-scrollbar-thumb-hover` 绑定到 l1（基础表面）token，两条渲染路径都读取这一组变量。抬升表面（菜单、浮层、对话框）在自己的容器上设置 `--dsh-scrollbar-thumb: var(--dsw-alias-scrollbar-bg-l2)` 与 `--dsh-scrollbar-thumb-hover: var(--dsw-alias-scrollbar-hover-l2)`；一次重新绑定即可为引擎实际走的那条路径换色。
两条路径在构造上互斥。`scrollbar-width`／`scrollbar-color` 写在 `@supports not selector(::-webkit-scrollbar)` 之内，因为这两个属性只要取非 `auto` 值，Chromium 与 Safari 就会丢弃该元素上的全部 `::-webkit-scrollbar*` 规则，`::-webkit-scrollbar-thumb:hover` 也在其中——若无条件地同时声明，`--dsh-scrollbar-thumb-hover` 在任何引擎上都不会被渲染。因此 Firefox 走标准属性，WebKit 系引擎走伪元素，hover token 只经由伪元素这条路径渲染。推理过程与实测计算值见[滚动条 Agent Note](../../../.agents/notes/implemented/bug-fix/2026-07-28-themed-scrollbars-and-reserved-gutter.md)。
## 模型体验