Add the containment group's stylesheet test harness

tests/Feature/Components/ContainmentStylesheetsTest.php is the
containment twin of InputStylesheetsTest.php and ActionStylesheetsTest.php:
same shape, import and ViewClasses checks, keyed on the "Containment"
block of components.css. Its dataset starts empty and grows by one name
per component commit in this stream (plan step 36).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

tests/Feature/Components/ContainmentStylesheetsTest.php

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+<?php
+
+use Illuminate\Support\Facades\File;
+use NoNameWeb\LivewireMaterial\Tests\Support\ComponentStylesheet;
+use NoNameWeb\LivewireMaterial\Tests\Support\ViewClasses;
+
+/**
+ * The containment components, rewritten without Tailwind (plan step 36): each view renders
+ * `data-md-*` attributes and no class list of its own beyond the interaction and text classes
+ * (tests/Support/ViewClasses.php), and each has a stylesheet in `material.components` that imports
+ * the stylesheets of the components its view renders, writes its values from the tokens and its
+ * breakpoints as px range queries, and is imported from the "Containment" block of components.css.
+ *
+ * The dataset grows by one name per component commit (`divider`, `collapse`, `card`, then `list`
+ * and `list-item` together), the same rule InputStylesheetsTest.php and ActionStylesheetsTest.php
+ * follow. It starts empty: this file lands before any containment component is rewritten.
+ */
+dataset('containment components', [
+    //
+]);
+
+/**
+ * Fails unless every media query in the stylesheet writes its lengths in px, at one of M3's four
+ * breakpoints. `rem` and `em` would grow with the reader's text size, which a breakpoint must not.
+ */
+function assertContainmentBreakpointsInPx(ComponentStylesheet $css, string $label): void
+{
+    foreach ($css->mediaQueries() as $query) {
+        preg_match_all('/\(([^()]*)\)/', $query, $features);
+
+        foreach ($features[1] as $feature) {
+            preg_match_all('/(\d*\.?\d+)(px|rem|em)\b/', $feature, $lengths, PREG_SET_ORDER);
+
+            foreach ($lengths as [, $number, $unit]) {
+                expect($unit)->toBe('px', "{$label}: {$query}");
+                expect(in_array($number, ['600', '840', '1200', '1600'], true))->toBeTrue("{$label}: {$query} is not at an M3 breakpoint");
+            }
+        }
+    }
+}
+
+/**
+ * Colours are roles, shadows are elevation levels or a ring, type is a type style, and breakpoints
+ * are px, at one of M3's four.
+ */
+function assertContainmentTokensAndPxBreakpoints(ComponentStylesheet $css, string $label): void
+{
+    $source = (string) preg_replace('~/\*.*?\*/~s', '', $css->css);
+
+    expect($source)->not->toMatch('/#[0-9a-f]{3,8}\b|\b(?:rgba?|hsla?|oklch|oklab|lab|lch)\(/i')
+        ->not->toMatch('/\bfont:(?!\s*var\(--md-sys-typescale-)/')
+        ->not->toMatch('/\btransition[a-z-]*:[^;]*(?:\d+m?s\b|\bease\b|ease-in|ease-out|cubic-bezier)/');
+
+    // A box-shadow is `none`, an elevation level, or a ring: `[inset] 0 0 0 <n>px` in a colour role.
+    $colour = 'var\(--md-sys-color-[a-z-]+\)|color-mix\(in srgb, var\(--md-sys-color-[a-z-]+\) [^;]+?, transparent\)';
+
+    preg_match_all('/\bbox-shadow:\s*([^;]+);/', $source, $shadows, PREG_SET_ORDER);
+
+    foreach ($shadows as [, $value]) {
+        expect(trim($value))->toMatch("/^(?:none|var\\(--md-sys-elevation-[0-5]\\)|(?:inset )?0 0 0 \\d+px (?:{$colour}))$/", "{$label}: box-shadow: {$value} is not none, an elevation or a ring in a colour role");
+    }
+
+    assertContainmentBreakpointsInPx($css, $label);
+}
+
+it('draws the component from a stylesheet shaped like every package stylesheet', function (string $name) {
+    $css = ComponentStylesheet::read($name);
+
+    expect($css->css)->toStartWith('/*')
+        ->and($css->statements()[0] ?? null)->toBe('@layer material.reset, material.tokens, material.base, material.layout, material.components, material.text, material.visibility;')
+        ->and(array_slice($css->statements(), 1))->each->toMatch('/^@import \'\.\/[a-z-]+\.css\';$/')
+        ->and($css->blocks())->each->toBe('@layer material.components')
+        ->and($css->css)->not->toMatch('/@(?:tailwind|theme|utility|variant|custom-variant|apply|source|config|plugin|reference)\b|--(?:theme|spacing|alpha)\(|\btheme\(/');
+
+    foreach ($css->imports() as $import) {
+        expect(is_file(dirname(ComponentStylesheet::path($name)).'/'.$import))->toBeTrue("{$name}.css imports {$import}, which does not exist");
+    }
+})->with('containment components');
+
+it('imports the stylesheet of every component its view renders', function (string $name) {
+    preg_match_all('/<x-livewire-material::([a-z-]+)/', File::get(__DIR__."/../../../resources/views/components/{$name}.blade.php"), $tags);
+
+    $rendered = collect($tags[1])->unique()
+        // A component still written for Tailwind has no stylesheet of its own to import yet; its
+        // old stylesheet, if it has one, lives in tailwind.css without the layer statement.
+        ->filter(fn (string $tag): bool => is_file(ComponentStylesheet::path($tag)) && str_contains(File::get(ComponentStylesheet::path($tag)), '@layer material.components'))
+        ->map(fn (string $tag): string => "./{$tag}.css")
+        ->values()
+        ->all();
+
+    expect(array_values(array_diff($rendered, ComponentStylesheet::read($name)->imports())))->toBe([]);
+})->with('containment components');
+
+it('writes no class list into the view but the interaction and text classes', function (string $name) {
+    expect(ViewClasses::violations(File::get(__DIR__."/../../../resources/views/components/{$name}.blade.php")))->toBe([]);
+})->with('containment components');
+
+it('takes its values from the tokens and its breakpoints in px', function (string $name) {
+    assertContainmentTokensAndPxBreakpoints(ComponentStylesheet::read($name), "{$name}.css");
+})->with('containment components');
+
+it('is imported from the containment block of components.css', function (string $name) {
+    $components = File::get(__DIR__.'/../../../resources/css/components.css');
+    $block = substr($components, (int) strpos($components, '/* Containment */'));
+    $block = substr($block, 0, (int) strpos($block, '/* Navigation */'));
+
+    expect($block)->toContain("@import './components/{$name}.css';");
+})->with('containment components');