diff --git a/apps/docs/src/style-matrix.stories.tsx b/apps/docs/src/style-matrix.stories.tsx
new file mode 100644
index 0000000..92ab596
--- /dev/null
+++ b/apps/docs/src/style-matrix.stories.tsx
@@ -0,0 +1,231 @@
+import {
+  Button,
+  Card,
+  CardContent,
+  CardDescription,
+  CardHeader,
+  CardTitle,
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+  DialogTrigger,
+  Input,
+  Skeleton,
+  Switch,
+  skinDetails,
+  skinNames,
+  type SkinName
+} from "@ai-ui/ui";
+import type { Meta, StoryObj } from "@storybook/react";
+
+const motionModes = [
+  {
+    label: "System motion",
+    value: "system"
+  },
+  {
+    label: "Reduced motion",
+    value: "reduced"
+  }
+] as const;
+
+type MotionMode = (typeof motionModes)[number]["value"];
+
+function RuntimePill({ children }: { children: React.ReactNode }) {
+  return (
+    <span className="rounded-full border border-[var(--color-border)] bg-[var(--color-surface)] px-3 py-1 text-xs uppercase tracking-[var(--tracking-caps)] text-[var(--color-muted-foreground)]">
+      {children}
+    </span>
+  );
+}
+
+function PanelPreview() {
+  return (
+    <div
+      className="grid gap-3 border p-4"
+      style={{
+        background: "var(--ui-panel-bg)",
+        borderColor: "var(--ui-panel-border)",
+        borderRadius: "var(--ui-panel-radius)",
+        borderWidth: "var(--ui-panel-border-width)",
+        boxShadow: "var(--ui-panel-shadow)",
+        backdropFilter: "blur(var(--ui-panel-backdrop-blur))"
+      }}
+    >
+      <div className="flex items-start justify-between gap-3">
+        <div>
+          <p className="text-sm font-semibold text-[var(--color-foreground)]">
+            Dialog panel contract
+          </p>
+          <p className="mt-1 text-sm leading-6 text-[var(--color-muted-foreground)]">
+            Panel vars preview the dialog surface without opening an overlay in every
+            matrix cell.
+          </p>
+        </div>
+        <Button aria-hidden="true" size="icon" tabIndex={-1} variant="ghost">
+          ×
+        </Button>
+      </div>
+      <div className="grid gap-2">
+        <Skeleton shape="line" />
+        <Skeleton shape="block" />
+      </div>
+    </div>
+  );
+}
+
+function ComparisonCell({
+  motion,
+  skin
+}: {
+  motion: MotionMode;
+  skin: SkinName;
+}) {
+  return (
+    <section
+      className="grid gap-4 rounded-[var(--radius-lg)] border border-[var(--color-border)] bg-[var(--color-card)] p-4 shadow-[var(--shadow-sm)]"
+      data-motion={motion === "reduced" ? "reduced" : undefined}
+      data-skin={skin}
+    >
+      <div className="flex flex-wrap gap-2">
+        <RuntimePill>{skinDetails[skin].label}</RuntimePill>
+        <RuntimePill>{motion}</RuntimePill>
+      </div>
+
+      <Card interactive tone="default">
+        <CardHeader>
+          <CardTitle>Release routing</CardTitle>
+          <CardDescription>
+            The same component tree should now pick up distinct skin treatments.
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="grid gap-3">
+          <Input defaultValue="Launch notes approved" readOnly />
+          <div className="flex items-center justify-between gap-3">
+            <span className="text-sm text-[var(--color-muted-foreground)]">
+              Quiet notifications
+            </span>
+            <Switch checked />
+          </div>
+          <div className="flex flex-wrap gap-3">
+            <Button>Primary</Button>
+            <Button variant="secondary">Secondary</Button>
+            <Button variant="subtle">Subtle</Button>
+          </div>
+        </CardContent>
+      </Card>
+
+      <PanelPreview />
+    </section>
+  );
+}
+
+function MatrixDialogSandbox() {
+  return (
+    <Dialog>
+      <DialogTrigger asChild>
+        <Button variant="secondary">Open live dialog preview</Button>
+      </DialogTrigger>
+      <DialogContent>
+        <DialogHeader>
+          <DialogTitle>Dialog validation sandbox</DialogTitle>
+          <DialogDescription>
+            Use the Storybook toolbar to validate the real overlay under the active theme,
+            skin, and motion settings.
+          </DialogDescription>
+        </DialogHeader>
+        <DialogFooter>
+          <Button variant="ghost">Back</Button>
+          <Button>Approve</Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}
+
+function StyleMatrixShowcase() {
+  return (
+    <div className="min-h-screen bg-[var(--color-background)] px-6 py-10 text-[var(--color-foreground)] sm:px-10">
+      <div className="mx-auto flex w-full max-w-7xl flex-col gap-8">
+        <header className="max-w-4xl space-y-4">
+          <p className="text-sm uppercase tracking-[var(--tracking-caps)] text-[var(--color-muted-foreground)]">
+            AI UI / Phase 3
+          </p>
+          <h1
+            className="font-semibold tracking-[var(--tracking-tight)]"
+            style={{
+              fontFamily: "var(--font-display)",
+              fontSize: "var(--text-4xl)",
+              lineHeight: "var(--leading-tight)"
+            }}
+          >
+            Style matrix compares the same product surface across skin and motion scopes.
+          </h1>
+          <p className="max-w-3xl text-[var(--text-lg)] leading-[var(--leading-loose)] text-[var(--color-muted-foreground)]">
+            This page is the screenshot-friendly regression target for the pilot skin work.
+            The grid uses nested `data-skin` and `data-motion` scopes so the same building
+            blocks can be reviewed side by side.
+          </p>
+        </header>
+
+        <section className="grid gap-4">
+          {motionModes.map((motionMode) => (
+            <div key={motionMode.value} className="grid gap-3">
+              <div className="flex items-center justify-between gap-4">
+                <div>
+                  <h2 className="text-2xl font-semibold">{motionMode.label}</h2>
+                  <p className="mt-1 text-sm text-[var(--color-muted-foreground)]">
+                    `{motionMode.value === "reduced" ? 'data-motion="reduced"' : "default"}`
+                    {" "}
+                    on the wrapper scope.
+                  </p>
+                </div>
+              </div>
+              <div className="grid gap-4 xl:grid-cols-3">
+                {skinNames.map((skin) => (
+                  <ComparisonCell key={`${motionMode.value}-${skin}`} motion={motionMode.value} skin={skin} />
+                ))}
+              </div>
+            </div>
+          ))}
+        </section>
+
+        <section className="grid gap-4 rounded-[var(--radius-lg)] border border-[var(--color-border)] bg-[var(--color-card)] p-6 shadow-[var(--shadow-sm)] lg:grid-cols-[minmax(0,1fr)_auto] lg:items-center">
+          <div>
+            <h2 className="text-2xl font-semibold">Live overlay validation</h2>
+            <p className="mt-2 max-w-3xl text-sm leading-6 text-[var(--color-muted-foreground)]">
+              Dialog still portals to the document root, so compare its real overlay and
+              panel treatment with the Storybook toolbar. The matrix above covers scoped
+              inline regression. The control below covers the live overlay behavior.
+            </p>
+          </div>
+          <div className="flex justify-start lg:justify-end">
+            <MatrixDialogSandbox />
+          </div>
+        </section>
+      </div>
+    </div>
+  );
+}
+
+const meta = {
+  title: "Foundation/Style Matrix",
+  component: StyleMatrixShowcase,
+  parameters: {
+    docs: {
+      description: {
+        component:
+          "Phase 3 adds the regression-oriented comparison surface. Use this page for screenshots and visual review, then use the live dialog sandbox below to validate portal-driven overlays under the active toolbar settings."
+      }
+    }
+  }
+} satisfies Meta<typeof StyleMatrixShowcase>;
+
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const Overview: Story = {};
diff --git a/docs/rfcs/multi-style-architecture.md b/docs/rfcs/multi-style-architecture.md
index 5889084..9ccc80c 100644
--- a/docs/rfcs/multi-style-architecture.md
+++ b/docs/rfcs/multi-style-architecture.md
@@ -511,7 +511,7 @@ Deliverables:
 
 Status:
 
-- not started
+- completed
 
 ### Phase 4: Expand Coverage
 
@@ -605,7 +605,9 @@ As of 2026-03-20, the project is at this point:
 - docs switching surface added in `Foundation/Style Contract`
 - pilot recipe extraction completed for `Button`, `Card`, `Input`, `Dialog`, `Switch`,
   and `Skeleton`
+- screenshot-friendly validation surface added in `Foundation/Style Matrix`
+- scoped `data-motion="reduced"` now works for nested docs wrappers
 - broader component-library rollout still pending
 
-The next implementation task should be Phase 3: add a dedicated comparison-oriented docs
-validation surface for skins and motion modes.
+The next implementation task should be Phase 4: expand the skin-aware pattern across the
+broader component library.
diff --git a/packages/tokens/src/motion.css b/packages/tokens/src/motion.css
index 2a5a718..59af710 100644
--- a/packages/tokens/src/motion.css
+++ b/packages/tokens/src/motion.css
@@ -19,7 +19,8 @@
   --scale-pop: 1.02;
 }
 
-:root[data-motion="reduced"] {
+:root[data-motion="reduced"],
+[data-motion="reduced"] {
   --dur-instant: 1ms;
   --dur-fast: 1ms;
   --dur-base: 1ms;
@@ -32,6 +33,19 @@
   --scale-press: 1;
   --scale-hover: 1;
   --scale-pop: 1;
+  scroll-behavior: auto;
+}
+
+:root[data-motion="reduced"] *,
+:root[data-motion="reduced"] *::before,
+:root[data-motion="reduced"] *::after,
+[data-motion="reduced"] *,
+[data-motion="reduced"] *::before,
+[data-motion="reduced"] *::after {
+  animation-duration: 1ms !important;
+  animation-iteration-count: 1 !important;
+  scroll-behavior: auto !important;
+  transition-duration: 1ms !important;
 }
 
 @media (prefers-reduced-motion: reduce) {