collapse.css animated `<details>`' `::details-content` from `block-size: 0`
to `auto`, which needs `interpolate-size: allow-keywords` (Chrome 129 and
nothing else) and a `content-visibility` held through the close with
`allow-discrete` (not Firefox), so in Firefox and Safari the section
snapped open and shut. No stylesheet can do it there.
resources/js/collapse.js animates the `<details>` itself, the same way
in every engine: a Web Animation of its `block-size` from the height it
is drawn at to the height it is going to, on the fast spatial spring's
tokens, with `overflow: clip` and a `min-block-size` that keeps the
summary whole through the spring's overshoot, all inside the keyframes,
so nothing is left in `style`. Content below moves with it. Opening sets
`open` at once and grows the height; closing keeps `open` while the
height goes, marks `data-md-collapse-closing` so the chevron turns back
at the start, and drops `open` (and fires `toggle`) when the height has.
A press mid-way turns it round from the height it has reached. The CSS
animation is gone, so Chrome takes the same path and never animates
twice.
Routes: a press on the summary (pointer, Enter, Space) is taken over;
the Alpine and Livewire bindings call `materialCollapse()` from the
view's `x-effect` (its first call, as Alpine starts, sets the state at
once); a `name` group's open member closes on the same spring, its
`name` lifted for the close so the browser's exclusivity does not shut
it first and put back once closed. Anything else that sets `open`
(find-in-page, an application's own script) stays instant, as the
browser draws it, and is followed. Under reduced motion every route is
the browser's own.
Browser tests in Chrome, Firefox and Safari catch the height part-way
open and shut (and what is under it moving) from a press and from the
Alpine binding, the chevron turning at the start of a close, the clip
while it moves, Enter on the summary, a reversal mid-way, a name group,
and reduced motion. The four motion tests fail on main in Firefox and
Safari.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Plan step 36 review of 76abdd62. The old view put the filled variant's
16px padding on its own summary and body; the stylesheet matched them as
descendants of any filled collapse, so a plain collapse nested inside
one took the padding too (and an open one turned every nested chevron).
Child combinators now tie each rule to its own <details>. The 12px gap is
a literal like alert.css's, not an average of two spacing tokens.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
Plan step 36 (containment group): <x-collapse>'s Tailwind-era
resources/css/components/collapse.css (the height animation, C-24)
becomes the plain stylesheet, keyed on data-md-collapse and
data-md-variant; the summary renders the shared md-state-layer and
md-focus-ring classes instead of copying their rules. Leaves
tailwind.css for the Containment block of components.css.
Icon-to-title and title-to-chevron gaps stay 12px (not an M3 number;
collapse isn't an M3 component), written as the average of the two
adjacent spacing steps since the scale has no exact token for it.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
Plan step 19, containment.md C-24. `interpolate-size: allow-keywords`
was set and nothing transitioned, so the content snapped open. A new
resources/css/components/collapse.css transitions `block-size` on
`::details-content` over the fast spatial spring, with
`content-visibility` `allow-discrete` beside it so the section stays
rendered while it closes. The `<details>` carries `data-collapse` for
the rule to find.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
