Rewrite the collapse without Tailwind

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

resources/css/components/collapse.css

@@ -1,22 +1,42 @@
 /*
- * `<x-collapse>`'s height, eased open.
+ * <x-collapse>: not an M3 component — M3 has expandable list items and menu expansion but no
+ * standalone disclosure — built on the native `<details>` so it opens without script, keeps its
+ * state through a Livewire morph, and is announced as a disclosure by the browser. Judged against
+ * foundations rather than any M3 component spec (docs/audits/m3-alignment/containment.md, C-24).
  *
- * The native `<details>` opens and closes by itself; what it cannot do on its own is animate, so
- * the component sets `interpolate-size: allow-keywords` (which makes `0` → `auto` an animatable
- * pair) and this transitions `block-size` on `::details-content`, the pseudo-element that holds
- * everything after the `<summary>`. `content-visibility` goes with it, `allow-discrete`, so the
- * content stays rendered while it closes rather than vanishing on the first frame.
+ * `interpolate-size: allow-keywords` makes `<details>`'s `0 -> auto` block-size an animatable pair,
+ * so `::details-content` (the pseudo-element that holds everything after the summary) can transition
+ * `block-size` on the fast spatial spring, the same one that turns the chevron; `content-visibility`
+ * goes with it, `allow-discrete`, so the content stays rendered while it closes rather than
+ * vanishing on the first frame. Under reduced motion the duration token is zero
+ * (tokens/motion.css), so the section snaps open with nothing else to do.
  *
- * The fast spatial spring, as the chevron beside it: M3's spatial track is for anything that
- * changes size or position. Under reduced motion the duration token is zero
- * (resources/css/tokens/motion.css), so the section snaps open with nothing else to do.
+ * `data-md-variant="filled"` is a surface-container tile with a large corner; the summary inherits
+ * it (`border-radius: inherit`) so the shared `md-state-layer`'s own `::before`, which also
+ * inherits, draws inside the same shape. `md-state-layer` and `md-focus-ring`
+ * (foundation/interaction.css) sit on the summary; this file only refines their target — the
+ * 48px summary height, the icon and chevron colour — never their opacities or ring.
  *
- * Not an M3 component — M3 has expandable list items and menu expansion, no standalone disclosure
- * — so the geometry is the library's and only the motion tokens are M3's.
+ * Icon-to-title and title-to-chevron gaps are 12px, midway between two spacing steps
+ * (`space100` 8px, `space200` 16px); written as their average rather than a bare literal so the
+ * value still comes from the scale.
  */
 
-@layer components {
-    [data-collapse]::details-content {
+@layer material.reset, material.tokens, material.base, material.layout, material.components, material.text, material.visibility;
+
+@import './icon.css';
+
+@layer material.components {
+    [data-md-collapse] {
+        interpolate-size: allow-keywords;
+    }
+
+    [data-md-collapse][data-md-variant='filled'] {
+        border-radius: var(--md-sys-shape-corner-lg);
+        background-color: var(--md-sys-color-surface-container);
+    }
+
+    [data-md-collapse]::details-content {
         block-size: 0;
         overflow: hidden;
         transition:
@@ -24,7 +44,56 @@
             content-visibility var(--md-sys-motion-spatial-fast-duration) allow-discrete;
     }
 
-    [data-collapse][open]::details-content {
+    [data-md-collapse][open]::details-content {
         block-size: auto;
     }
+
+    [data-md-collapse-summary] {
+        display: flex;
+        min-block-size: var(--md-sys-measurement-space600);
+        align-items: center;
+        gap: calc((var(--md-sys-measurement-space100) + var(--md-sys-measurement-space200)) / 2);
+        border-radius: inherit;
+        cursor: pointer;
+        list-style-type: none;
+        font: var(--md-sys-typescale-title-md);
+        letter-spacing: var(--md-sys-typescale-title-md-tracking);
+
+        &::-webkit-details-marker {
+            display: none;
+        }
+    }
+
+    [data-md-collapse][data-md-variant='filled'] [data-md-collapse-summary] {
+        padding-inline: var(--md-sys-measurement-space200);
+    }
+
+    [data-md-collapse-icon] {
+        color: var(--md-sys-color-on-surface-variant);
+    }
+
+    [data-md-collapse-title] {
+        min-width: 0;
+        flex: 1 1 0%;
+    }
+
+    [data-md-collapse-chevron] {
+        color: var(--md-sys-color-on-surface-variant);
+        transition: rotate var(--md-sys-motion-spatial-fast-duration) var(--md-sys-motion-spatial-fast);
+    }
+
+    [data-md-collapse][open] [data-md-collapse-chevron] {
+        rotate: 180deg;
+    }
+
+    [data-md-collapse-body] {
+        padding-block: var(--md-sys-measurement-space50) var(--md-sys-measurement-space200);
+        color: var(--md-sys-color-on-surface-variant);
+        font: var(--md-sys-typescale-body-md);
+        letter-spacing: var(--md-sys-typescale-body-md-tracking);
+    }
+
+    [data-md-collapse][data-md-variant='filled'] [data-md-collapse-body] {
+        padding-inline: var(--md-sys-measurement-space200);
+    }
 }