diff --git a/src/app/dev/buttons/page.tsx b/src/app/dev/buttons/page.tsx
new file mode 100644
index 0000000..5c63d78
--- /dev/null
+++ b/src/app/dev/buttons/page.tsx
@@ -0,0 +1,19 @@
+// Dev-only story page for the button system (task jhxk68cdy). Not linked from
+// the app and returns 404 in production builds. Shows every style in both themes.
+import type { CSSProperties } from "react";
+import { notFound } from "next/navigation";
+import { ButtonGallery } from "@/components/ButtonGallery";
+
+export const metadata = { title: "Buttons (dev)" };
+
+const grid: CSSProperties = { display: "grid", gridTemplateColumns: "repeat(auto-fit, minmax(340px, 1fr))", minHeight: "100vh" };
+
+export default function ButtonsDevPage() {
+  if (process.env.NODE_ENV === "production") notFound();
+  return (
+    <main style={grid}>
+      <ButtonGallery theme="dark" />
+      <ButtonGallery theme="light" />
+    </main>
+  );
+}
diff --git a/src/app/globals.css b/src/app/globals.css
index 6a8e0bf..55ebebe 100644
--- a/src/app/globals.css
+++ b/src/app/globals.css
@@ -1,9 +1,11 @@
 /* Global styles only (ADR 0001, section 6): layer order, tokens, reset, focus ring. */
 @layer reset, base;
 
-/* Tokens. Dark is the default, so it applies even without data-theme. */
+/* Tokens. Dark is the default, so it applies even without data-theme.
+   A nested [data-theme] element re-scopes the theme tokens (used by the dev button page). */
 :root,
-:root[data-theme="dark"] {
+:root[data-theme="dark"],
+[data-theme="dark"] {
   --bg: #09090B;
   --tile: #121215;
   --tile-2: #19191D;
@@ -17,10 +19,16 @@
   --danger: #FF6B70;
   --glass: rgba(18,18,21,.72);
   --shadow-pop: 0 10px 28px rgba(0,0,0,.5);
+  /* Buttons: drop shadows and the soft-depth (neumorphic) light and shade. */
+  --shadow-btn: 0 10px 20px -6px rgba(0,0,0,.35);
+  --shadow-float: 0 14px 28px -12px rgba(0,0,0,.55);
+  --neu-d: rgba(0,0,0,.8);
+  --neu-l: rgba(255,255,255,.05);
   color-scheme: dark;
 }
 
-:root[data-theme="light"] {
+:root[data-theme="light"],
+[data-theme="light"] {
   --bg: #EFEDE9;
   --tile: #FBFAF8;
   --tile-2: #F3F1EE;
@@ -34,6 +42,10 @@
   --danger: #B3121A;
   --glass: rgba(251,250,248,.74);
   --shadow-pop: 0 10px 28px rgba(26,28,31,.14);
+  --shadow-btn: 0 10px 20px -6px rgba(26,28,31,.22);
+  --shadow-float: 0 14px 28px -12px rgba(26,28,31,.3);
+  --neu-d: rgba(26,28,31,.17);
+  --neu-l: rgba(255,255,255,.95);
   color-scheme: light;
 }
 
@@ -42,6 +54,11 @@
   --accent-hi: color-mix(in srgb, var(--accent), white 26%);
   --accent-lo: color-mix(in srgb, var(--accent), black 30%);
   --accent-soft: color-mix(in srgb, var(--accent), transparent 88%);
+  --accent-deep: color-mix(in srgb, var(--accent), black 55%);
+  --accent-glow: rgba(255,110,110,.75);
+  --accent-glow-0: rgba(255,110,110,0);
+  /* Text and marks on a crimson face: white in both themes. */
+  --on-accent: #FFFFFF;
 
   /* HexAvatar initials: dark muted gradients, same in both themes. */
   --hex-oxblood: linear-gradient(145deg, #6e1a22, #3a0d12);
diff --git a/src/app/layout.tsx b/src/app/layout.tsx
index c8b6545..e5b3f64 100644
--- a/src/app/layout.tsx
+++ b/src/app/layout.tsx
@@ -4,6 +4,7 @@ import { Cormorant_Garamond, Manrope } from "next/font/google";
 import { DEFAULT_THEME, THEME_SCRIPT } from "@/lib/theme";
 import "./globals.css";
 import "../styles/type.css";
+import "../styles/buttons.css";
 import "../styles/avatar.css";
 import "../styles/legacy.css";
 
diff --git a/src/components/ButtonGallery.tsx b/src/components/ButtonGallery.tsx
new file mode 100644
index 0000000..dc7f109
--- /dev/null
+++ b/src/components/ButtonGallery.tsx
@@ -0,0 +1,79 @@
+// Every button style and state, in one theme scope. Used by the dev story page
+// (src/app/dev/buttons) and the button tests.
+import type { CSSProperties, ReactNode } from "react";
+import type { Theme } from "@/lib/theme";
+import { DepthButton, FlipButton, GrowButton, IconButton, SendIcon, SparkleButton, SweepButton } from "./Buttons";
+
+const scope: CSSProperties = {
+  background: "var(--bg)",
+  color: "var(--ink)",
+  padding: "32px 28px",
+  display: "flex",
+  flexDirection: "column",
+  gap: 28,
+};
+const row: CSSProperties = { display: "flex", flexWrap: "wrap", alignItems: "center", gap: 14 };
+const heading: CSSProperties = { margin: "0 0 10px", fontSize: 12, fontWeight: 700, letterSpacing: ".12em", textTransform: "uppercase", color: "var(--ink-3)" };
+
+function Section({ title, children }: { title: string; children: ReactNode }) {
+  return (
+    <section>
+      <h2 style={heading}>{title}</h2>
+      <div style={row}>{children}</div>
+    </section>
+  );
+}
+
+const FlameIcon = (
+  <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={1.7} strokeLinecap="round" strokeLinejoin="round">
+    <path d="M12 21c4 0 7-2.8 7-6.8 0-4.5-4-6.7-5-11.2-2.3 1.7-3.5 4-3.2 6.5C9.5 9 8.6 8 8.3 6.6 6.3 8.5 5 10.9 5 14.2 5 18.2 8 21 12 21z" />
+  </svg>
+);
+const TrashIcon = (
+  <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={1.8} strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+    <path d="M4 7h16M9 7V4.5h6V7M6.5 7l1 13h9l1-13" />
+  </svg>
+);
+const PlayIcon = (
+  <svg viewBox="0 0 24 24" aria-hidden="true">
+    <path d="M8 5.5v13l11-6.5z" fill="currentColor" />
+  </svg>
+);
+
+export function ButtonGallery({ theme }: { theme: Theme }) {
+  return (
+    <div data-theme={theme} style={scope} aria-label={`Buttons, ${theme} theme`} role="region">
+      <h1 className="type-title type-title-strong" style={{ margin: 0 }}>
+        {theme === "dark" ? "Dark" : "Light"} theme
+      </h1>
+      <Section title="Flip reveal: ready, disabled, posting">
+        <FlipButton state="ready" type="button" />
+        <FlipButton state="disabled" type="button" />
+        <FlipButton state="posting" type="button" />
+      </Section>
+      <Section title="Circle expand">
+        <GrowButton label="3 new posts" />
+      </Section>
+      <Section title="Outline fill sweep">
+        <SweepButton label="Business" selected />
+        <SweepButton label="Media" selected={false} />
+        <SweepButton label="Cancel" />
+      </Section>
+      <Section title="Soft depth, rising liquid">
+        <div style={{ width: 280 }}>
+          <DepthButton label="Trending minnects" sublabel="What people are watching" icon={FlameIcon} />
+        </div>
+      </Section>
+      <Section title="Sparkle glow: sign in, mobile new post">
+        <SparkleButton label="Sign in" />
+        <SparkleButton variant="fab" label="New post" />
+      </Section>
+      <Section title="Glossy crimson icon button">
+        <IconButton label="Send comment" icon={<SendIcon />} />
+        <IconButton label="Delete post" icon={TrashIcon} size="sm" />
+        <IconButton label="Play video" icon={PlayIcon} shape="round" />
+        <IconButton label="Send comment (disabled)" icon={<SendIcon />} disabled />
+      </Section>
+    </div>
+  );
+}
diff --git a/src/components/Buttons.tsx b/src/components/Buttons.tsx
new file mode 100644
index 0000000..8ce2346
--- /dev/null
+++ b/src/components/Buttons.tsx
@@ -0,0 +1,239 @@
+// Button system (spec "Buttons", ADR 0001). Styles live in src/styles/buttons.css.
+// Each component renders a native <button>; extra button props pass through.
+import type { ButtonHTMLAttributes, ReactNode } from "react";
+
+type NativeButton = Omit<ButtonHTMLAttributes<HTMLButtonElement>, "children">;
+
+const cx = (...parts: Array<string | false | null | undefined>) => parts.filter(Boolean).join(" ");
+
+const svgProps = {
+  viewBox: "0 0 24 24",
+  fill: "none",
+  stroke: "currentColor",
+  strokeLinecap: "round" as const,
+  strokeLinejoin: "round" as const,
+  "aria-hidden": true,
+};
+
+export function SendIcon() {
+  return (
+    <svg {...svgProps} strokeWidth={2}>
+      <path d="M21 3 10.5 13.5" />
+      <path d="M21 3 14.5 21l-4-7.5L3 9.5z" />
+    </svg>
+  );
+}
+
+export function ArrowUpIcon() {
+  return (
+    <svg {...svgProps} strokeWidth={2.4}>
+      <path d="M12 19V5M6 11l6-6 6 6" />
+    </svg>
+  );
+}
+
+export function PlusIcon() {
+  return (
+    <svg {...svgProps} strokeWidth={2.2}>
+      <path d="M12 5v14M5 12h14" />
+    </svg>
+  );
+}
+
+/* 1. Flip reveal ------------------------------------------------------- */
+
+export type FlipState = "ready" | "disabled" | "posting";
+
+export interface FlipButtonProps extends NativeButton {
+  state?: FlipState;
+  /** Face label in the ready and disabled states. */
+  label?: string;
+  /** Panel that slides up on hover when ready. */
+  hoverLabel?: string;
+  /** Panel that slides up on hover when there is nothing to post. */
+  disabledLabel?: string;
+  /** Face label while posting. */
+  busyLabel?: string;
+}
+
+/** The labels each state shows: face text, hover panel text, and whether the send icon shows. */
+export function flipLabels(
+  state: FlipState,
+  labels: { label?: string; hoverLabel?: string; disabledLabel?: string; busyLabel?: string } = {},
+) {
+  const { label = "Post", hoverLabel = "Publish", disabledLabel = "Write first", busyLabel = "Posting" } = labels;
+  if (state === "posting") return { front: busyLabel, back: null, icon: false };
+  if (state === "disabled") return { front: label, back: disabledLabel, icon: false };
+  return { front: label, back: hoverLabel, icon: true };
+}
+
+export function FlipButton({
+  state = "ready",
+  label,
+  hoverLabel,
+  disabledLabel,
+  busyLabel,
+  className,
+  type = "submit",
+  disabled,
+  ...rest
+}: FlipButtonProps) {
+  const { front, back, icon } = flipLabels(state, { label, hoverLabel, disabledLabel, busyLabel });
+  const busy = state === "posting";
+  return (
+    <button
+      {...rest}
+      type={type}
+      className={cx("btn-flip", busy && "btn-flip-busy", className)}
+      disabled={disabled || state !== "ready"}
+      aria-busy={busy || undefined}
+    >
+      <span className="btn-flip-front">
+        {front}
+        {icon ? <SendIcon /> : null}
+      </span>
+      {back ? (
+        <span className="btn-flip-back" aria-hidden="true">
+          {back}
+          {icon ? <SendIcon /> : null}
+        </span>
+      ) : null}
+    </button>
+  );
+}
+
+/* 2. Circle expand ----------------------------------------------------- */
+
+export interface GrowButtonProps extends NativeButton {
+  label: string;
+  icon?: ReactNode;
+}
+
+export function GrowButton({ label, icon, className, type = "button", ...rest }: GrowButtonProps) {
+  return (
+    <button {...rest} type={type} className={cx("btn-grow", className)}>
+      <span className="btn-grow-circle" aria-hidden="true">
+        {icon ?? <ArrowUpIcon />}
+      </span>
+      <span className="btn-grow-text">{label}</span>
+    </button>
+  );
+}
+
+/* 3. Outline fill sweep ------------------------------------------------ */
+
+export interface SweepButtonProps extends NativeButton {
+  label: string;
+  /** Selected chip: stays filled. Sets aria-pressed when given. */
+  selected?: boolean;
+}
+
+export function SweepButton({ label, selected, className, type = "button", ...rest }: SweepButtonProps) {
+  return (
+    <button
+      {...rest}
+      type={type}
+      className={cx("btn-sweep", selected && "btn-sweep-on", className)}
+      aria-pressed={selected === undefined ? undefined : selected}
+    >
+      {label}
+    </button>
+  );
+}
+
+/* 4. Soft depth, rising liquid ----------------------------------------- */
+
+export interface DepthButtonProps extends NativeButton {
+  label: string;
+  sublabel?: string;
+  icon?: ReactNode;
+  /** Trailing content, for example a chevron or the current theme name. */
+  trailing?: ReactNode;
+}
+
+export function DepthButton({ label, sublabel, icon, trailing, className, type = "button", ...rest }: DepthButtonProps) {
+  return (
+    <button {...rest} type={type} className={cx("btn-depth", className)}>
+      {icon ? (
+        <span className="btn-depth-icon" aria-hidden="true">
+          {icon}
+        </span>
+      ) : null}
+      <span className="btn-depth-text">
+        <strong className="btn-depth-label">{label}</strong>
+        {sublabel ? <span className="btn-depth-sub">{sublabel}</span> : null}
+      </span>
+      {trailing}
+    </button>
+  );
+}
+
+/* 5. Sparkle glow ------------------------------------------------------ */
+
+const SPARKS = Array.from({ length: 10 }, (_, i) => i);
+
+function Sparks() {
+  return (
+    <span className="btn-spark-pts" aria-hidden="true">
+      {SPARKS.map((i) => (
+        <i key={i} />
+      ))}
+    </span>
+  );
+}
+
+export interface SparkleButtonProps extends NativeButton {
+  /** "signin": folded corner and hexagon icon. "fab": mobile new-post, plus icon only. */
+  variant?: "signin" | "fab";
+  /** Visible text for "signin"; accessible name for "fab". */
+  label: string;
+}
+
+export function SparkleButton({ variant = "signin", label, className, type = "button", ...rest }: SparkleButtonProps) {
+  if (variant === "fab") {
+    return (
+      <button {...rest} type={type} aria-label={label} className={cx("btn-spark", "btn-spark-fab", className)}>
+        <Sparks />
+        <span className="btn-spark-plus">
+          <PlusIcon />
+        </span>
+      </button>
+    );
+  }
+  return (
+    <button {...rest} type={type} className={cx("btn-spark", className)}>
+      <span className="btn-spark-fold" aria-hidden="true" />
+      <Sparks />
+      <span className="btn-spark-inner">
+        <svg className="btn-spark-hex" viewBox="0 0 24 24" aria-hidden="true">
+          <polygon points="12 2 20.66 7 20.66 17 12 22 3.34 17 3.34 7" />
+        </svg>
+        {label}
+      </span>
+    </button>
+  );
+}
+
+/* Glossy crimson icon button ------------------------------------------- */
+
+export interface IconButtonProps extends NativeButton {
+  /** Accessible name; the button shows only the icon. */
+  label: string;
+  icon: ReactNode;
+  shape?: "square" | "round";
+  size?: "md" | "sm";
+}
+
+export function IconButton({ label, icon, shape = "square", size = "md", className, type = "button", ...rest }: IconButtonProps) {
+  return (
+    <button
+      {...rest}
+      type={type}
+      aria-label={label}
+      title={rest.title ?? label}
+      className={cx("btn-gloss", shape === "round" && "btn-gloss-round", size === "sm" && "btn-gloss-sm", className)}
+    >
+      {icon}
+    </button>
+  );
+}
diff --git a/src/styles/buttons.css b/src/styles/buttons.css
new file mode 100644
index 0000000..7fce46a
--- /dev/null
+++ b/src/styles/buttons.css
@@ -0,0 +1,492 @@
+/*
+ * Button system (spec "Buttons", ADR 0001 sections 6 to 8).
+ * Five styles plus the glossy crimson icon button, ported from the mockup's
+ * recolored rules. Tokens only; white and black appear only on crimson faces.
+ * Every class sets margin, padding, font and color itself so the legacy
+ * `button` rules and any `button { color: inherit }` never leak in.
+ */
+
+/* Shared base for every style. */
+.btn-flip,
+.btn-grow,
+.btn-sweep,
+.btn-depth,
+.btn-spark,
+.btn-gloss {
+  appearance: none;
+  margin: 0;
+  border: 0;
+  font-family: inherit;
+  cursor: pointer;
+  position: relative;
+  overflow: hidden;
+  isolation: isolate;
+  opacity: 1;
+  -webkit-tap-highlight-color: transparent;
+}
+.btn-flip svg,
+.btn-grow svg,
+.btn-depth svg,
+.btn-spark svg,
+.btn-gloss svg { flex: none; }
+
+/* 1. Flip reveal: Post. Ready, disabled ("write first") and busy ("posting"). */
+.btn-flip {
+  height: 42px;
+  min-width: 118px;
+  padding: 0 22px;
+  border-radius: var(--r-ctl);
+  background: var(--ink);
+  color: var(--bg);
+  font-size: 13px;
+  font-weight: 800;
+  letter-spacing: .14em;
+  text-transform: uppercase;
+  box-shadow: var(--shadow-btn);
+  transition: transform .3s cubic-bezier(.23,1,.32,1);
+}
+.btn-flip .btn-flip-front {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+  height: 100%;
+  color: var(--bg);
+  transition: transform .6s cubic-bezier(.23,1,.32,1);
+}
+.btn-flip .btn-flip-back {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+  color: var(--on-accent);
+  background: linear-gradient(135deg, var(--accent-deep), var(--accent));
+  transform: translateY(100%);
+  transition: transform .6s cubic-bezier(.23,1,.32,1);
+}
+.btn-flip svg { width: 16px; height: 16px; }
+.btn-flip:hover .btn-flip-front,
+.btn-flip:focus-visible .btn-flip-front { transform: translateY(-200%); }
+.btn-flip:hover .btn-flip-back,
+.btn-flip:focus-visible .btn-flip-back { transform: none; }
+.btn-flip:active:not(:disabled) { transform: scale(.95); }
+
+/* Disabled: solid graphite face, readable text, never faded. */
+.btn-flip:disabled {
+  opacity: 1;
+  cursor: not-allowed;
+  background: var(--tile-3);
+  color: var(--ink-2);
+  box-shadow: inset 0 0 0 1px var(--line-2);
+}
+.btn-flip:disabled .btn-flip-front { color: var(--ink-2); }
+.btn-flip:disabled .btn-flip-back {
+  background: var(--tile-3);
+  color: var(--ink);
+  font-size: 12px;
+}
+
+/* Busy (posting): keeps the ink face, shows "Posting", never flips. */
+.btn-flip.btn-flip-busy:disabled {
+  cursor: progress;
+  background: var(--ink);
+  color: var(--bg);
+  box-shadow: var(--shadow-btn);
+}
+.btn-flip.btn-flip-busy:disabled .btn-flip-front { color: var(--bg); transform: none; }
+.btn-flip.btn-flip-busy .btn-flip-back { transform: translateY(100%); }
+
+/* 2. Circle expand: the new-posts pill. */
+.btn-grow {
+  display: block;
+  width: 178px;
+  height: 42px;
+  padding: 0;
+  border-radius: 999px;
+  background: var(--glass);
+  color: var(--ink);
+  -webkit-backdrop-filter: blur(16px);
+  backdrop-filter: blur(16px);
+  box-shadow: inset 0 0 0 1px var(--line-2), var(--shadow-float);
+}
+.btn-grow .btn-grow-circle {
+  position: absolute;
+  left: 4px;
+  top: 4px;
+  bottom: 4px;
+  width: 34px;
+  border-radius: 999px;
+  background: linear-gradient(180deg, var(--accent-hi), var(--accent) 55%, var(--accent-lo));
+  transition: width .45s cubic-bezier(.65,0,.076,1);
+}
+.btn-grow .btn-grow-circle svg {
+  position: absolute;
+  left: 9px;
+  top: 9px;
+  width: 16px;
+  height: 16px;
+  color: var(--on-accent);
+  transition: transform .45s cubic-bezier(.65,0,.076,1);
+}
+.btn-grow .btn-grow-text {
+  position: relative;
+  z-index: 1;
+  display: block;
+  padding-left: 40px;
+  line-height: 42px;
+  font-size: 11.5px;
+  font-weight: 800;
+  letter-spacing: .16em;
+  text-transform: uppercase;
+  white-space: nowrap;
+  color: var(--ink);
+  transition: color .45s cubic-bezier(.65,0,.076,1);
+}
+.btn-grow:hover .btn-grow-circle,
+.btn-grow:focus-visible .btn-grow-circle { width: calc(100% - 8px); }
+.btn-grow:hover .btn-grow-circle svg,
+.btn-grow:focus-visible .btn-grow-circle svg { transform: translateY(-3px); }
+.btn-grow:hover .btn-grow-text,
+.btn-grow:focus-visible .btn-grow-text { color: var(--on-accent); }
+.btn-grow:active { transform: scale(.97); }
+
+/* 3. Outline fill sweep: category chips and Cancel. Selected stays filled. */
+.btn-sweep {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  height: 34px;
+  padding: 0 15px;
+  border-radius: 999px;
+  background: transparent;
+  color: var(--ink);
+  font-size: 12.5px;
+  font-weight: 600;
+  white-space: nowrap;
+  box-shadow: inset 0 0 0 1.5px var(--line-2);
+  transition: color .3s, box-shadow .3s, transform .15s;
+}
+.btn-sweep::before {
+  content: "";
+  position: absolute;
+  z-index: -1;
+  width: 170px;
+  height: 170px;
+  border-radius: 50%;
+  background: var(--ink);
+  top: 100%;
+  left: 100%;
+  transition: top .35s var(--ease), left .35s var(--ease);
+}
+.btn-sweep:hover,
+.btn-sweep:focus-visible,
+.btn-sweep.btn-sweep-on {
+  color: var(--bg);
+  box-shadow: inset 0 0 0 1.5px var(--ink);
+}
+.btn-sweep:hover::before,
+.btn-sweep:focus-visible::before,
+.btn-sweep.btn-sweep-on::before { top: -70px; left: -40px; }
+.btn-sweep:active { transform: scale(.95); }
+
+/* 4. Soft depth, rising liquid: mobile More sheet rows and the theme switch. */
+.btn-depth {
+  display: flex;
+  align-items: center;
+  gap: 14px;
+  width: 100%;
+  padding: 14px;
+  border-radius: var(--r-card);
+  background: var(--bg);
+  color: var(--ink);
+  text-align: left;
+  font-size: 14px;
+  box-shadow: 6px 6px 14px var(--neu-d), -6px -6px 14px var(--neu-l);
+  transition: color .3s, box-shadow .25s;
+}
+.btn-depth::before,
+.btn-depth::after {
+  content: "";
+  position: absolute;
+  width: 140%;
+  height: 240%;
+  border-radius: 50%;
+  z-index: -1;
+  transition: all .5s .05s cubic-bezier(.55,0,.1,1);
+}
+.btn-depth::before {
+  left: 50%;
+  top: 100%;
+  transform: translateX(-50%) scaleX(1.25);
+  background: color-mix(in srgb, var(--accent), transparent 82%);
+}
+.btn-depth::after {
+  left: 55%;
+  top: 180%;
+  transform: translateX(-50%) scaleX(1.45);
+  background: var(--accent);
+}
+.btn-depth .btn-depth-icon {
+  width: 44px;
+  height: 44px;
+  flex: none;
+  display: grid;
+  place-items: center;
+  border-radius: var(--r-ctl);
+  background: var(--tile-2);
+  color: var(--ink);
+  transition: background-color .3s, color .3s;
+}
+.btn-depth .btn-depth-icon svg { width: 20px; height: 20px; }
+.btn-depth .btn-depth-text { flex: 1; min-width: 0; display: flex; flex-direction: column; gap: 2px; }
+.btn-depth .btn-depth-label { font-size: 15px; font-weight: 700; color: inherit; }
+.btn-depth .btn-depth-sub { font-size: 12.5px; color: var(--ink-3); transition: color .3s; }
+.btn-depth:hover,
+.btn-depth:focus-visible { color: var(--on-accent); }
+.btn-depth:hover::before,
+.btn-depth:focus-visible::before {
+  top: -35%;
+  background: var(--accent);
+  transform: translateX(-50%) scaleY(1.3) scaleX(.8);
+}
+.btn-depth:hover::after,
+.btn-depth:focus-visible::after { top: -45%; transform: translateX(-50%) scaleY(1.3) scaleX(.8); }
+.btn-depth:hover .btn-depth-sub,
+.btn-depth:focus-visible .btn-depth-sub { color: color-mix(in srgb, white 82%, transparent); }
+.btn-depth:hover .btn-depth-icon,
+.btn-depth:focus-visible .btn-depth-icon { background: color-mix(in srgb, white 16%, transparent); color: var(--on-accent); }
+.btn-depth:active { box-shadow: inset 4px 4px 12px var(--neu-d), inset -4px -4px 12px var(--neu-l); }
+
+/* 5. Sparkle glow: Sign in (fold + hexagon) and the mobile new-post button (plus). */
+.btn-spark {
+  --spark-round: 14px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 180px;
+  height: 50px;
+  padding: 0 22px;
+  border-radius: var(--spark-round);
+  color: var(--on-accent);
+  background:
+    radial-gradient(65% 65% at 50% 100%, var(--accent-glow) 0%, var(--accent-glow-0) 100%),
+    linear-gradient(0deg, var(--accent), var(--accent));
+  box-shadow: 0 18px 36px -14px color-mix(in srgb, var(--accent), transparent 15%);
+  transition: transform .25s;
+}
+.btn-spark::before,
+.btn-spark::after {
+  content: "";
+  position: absolute;
+  inset: var(--spark-inset);
+  border-radius: calc(var(--spark-round) - var(--spark-inset));
+  z-index: 0;
+  transition: all .5s ease-in-out;
+}
+.btn-spark::before {
+  --spark-inset: 1px;
+  background: linear-gradient(178deg, color-mix(in srgb, white 24%, transparent) 0%, transparent 100%);
+}
+.btn-spark::after {
+  --spark-inset: 2px;
+  background:
+    radial-gradient(65% 65% at 50% 100%, var(--accent-glow) 0%, var(--accent-glow-0) 100%),
+    linear-gradient(0deg, var(--accent), var(--accent));
+}
+.btn-spark:active { transform: scale(.96); }
+
+.btn-spark .btn-spark-fold {
+  z-index: 1;
+  position: absolute;
+  top: 0;
+  right: 0;
+  width: 1rem;
+  height: 1rem;
+  transition: all .5s ease-in-out;
+  background: radial-gradient(100% 75% at 55%, var(--accent-glow) 0%, var(--accent-glow-0) 100%);
+  box-shadow: 0 0 3px black;
+  border-bottom-left-radius: .5rem;
+  border-top-right-radius: var(--spark-round);
+}
+.btn-spark .btn-spark-fold::after {
+  content: "";
+  position: absolute;
+  top: 0;
+  right: 0;
+  width: 150%;
+  height: 150%;
+  transform: rotate(45deg) translateY(-18px);
+  background: var(--bg);
+  pointer-events: none;
+}
+.btn-spark:hover .btn-spark-fold,
+.btn-spark:focus-visible .btn-spark-fold { margin-top: -1rem; margin-right: -1rem; }
+
+.btn-spark .btn-spark-pts { position: absolute; inset: 0; overflow: hidden; pointer-events: none; z-index: 1; }
+.btn-spark .btn-spark-pts i {
+  position: absolute;
+  bottom: -10px;
+  width: 2px;
+  height: 2px;
+  border-radius: 50%;
+  background: var(--on-accent);
+  animation: btn-spark-rise infinite ease-in-out;
+}
+@keyframes btn-spark-rise {
+  0% { transform: translateY(0); }
+  85% { opacity: 0; }
+  100% { transform: translateY(-60px); opacity: 0; }
+}
+.btn-spark .btn-spark-pts i:nth-child(1) { left: 10%; animation-duration: 2.35s; animation-delay: .2s; }
+.btn-spark .btn-spark-pts i:nth-child(2) { left: 30%; opacity: .7; animation-duration: 2.5s; animation-delay: .5s; }
+.btn-spark .btn-spark-pts i:nth-child(3) { left: 25%; opacity: .8; animation-duration: 2.2s; animation-delay: .1s; }
+.btn-spark .btn-spark-pts i:nth-child(4) { left: 44%; opacity: .6; animation-duration: 2.05s; }
+.btn-spark .btn-spark-pts i:nth-child(5) { left: 50%; animation-duration: 1.9s; }
+.btn-spark .btn-spark-pts i:nth-child(6) { left: 75%; opacity: .5; animation-duration: 1.5s; animation-delay: 1.5s; }
+.btn-spark .btn-spark-pts i:nth-child(7) { left: 88%; opacity: .9; animation-duration: 2.2s; animation-delay: .2s; }
+.btn-spark .btn-spark-pts i:nth-child(8) { left: 58%; opacity: .8; animation-duration: 2.25s; animation-delay: .2s; }
+.btn-spark .btn-spark-pts i:nth-child(9) { left: 96%; opacity: .6; animation-duration: 2.6s; animation-delay: .1s; }
+.btn-spark .btn-spark-pts i:nth-child(10) { left: 65%; animation-duration: 2.5s; animation-delay: .2s; }
+
+.btn-spark .btn-spark-inner {
+  position: relative;
+  z-index: 2;
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  color: var(--on-accent);
+  font-weight: 700;
+  font-size: 15px;
+  letter-spacing: .06em;
+}
+.btn-spark .btn-spark-hex {
+  width: 18px;
+  height: 18px;
+  fill: transparent;
+  stroke: var(--on-accent);
+  stroke-width: 2.2;
+  stroke-linejoin: round;
+}
+.btn-spark:hover .btn-spark-hex,
+.btn-spark:focus-visible .btn-spark-hex {
+  animation: btn-spark-dash 1s linear forwards, btn-spark-fill .1s linear forwards .95s;
+}
+@keyframes btn-spark-dash { from { stroke-dasharray: 0 0 0 0; } to { stroke-dasharray: 68 68 0 0; } }
+@keyframes btn-spark-fill { to { fill: var(--on-accent); } }
+
+/* Mobile new-post variant: square, no fold, the plus turns 90 degrees. */
+.btn-spark.btn-spark-fab {
+  --spark-round: 16px;
+  min-width: 0;
+  width: 56px;
+  height: 56px;
+  padding: 0;
+  box-shadow: 0 12px 26px -10px color-mix(in srgb, var(--accent), transparent 15%);
+}
+.btn-spark.btn-spark-fab::after { display: none; }
+.btn-spark.btn-spark-fab:active { transform: scale(.94); }
+.btn-spark .btn-spark-plus {
+  position: relative;
+  z-index: 2;
+  width: 24px;
+  height: 24px;
+  color: var(--on-accent);
+  transition: transform .5s cubic-bezier(.2,.9,.3,1.4);
+}
+.btn-spark:hover .btn-spark-plus,
+.btn-spark:focus-visible .btn-spark-plus { transform: rotate(90deg); }
+
+/* Glossy crimson icon button: send comment, delete confirm, play. */
+.btn-gloss {
+  display: inline-grid;
+  place-items: center;
+  width: 44px;
+  height: 44px;
+  padding: 0;
+  border-radius: var(--r-ctl);
+  color: var(--on-accent);
+  background: linear-gradient(180deg, var(--accent-hi), var(--accent) 50%, var(--accent-lo));
+  box-shadow:
+    inset 0 1px 0 color-mix(in srgb, white 32%, transparent),
+    inset 0 -1px 0 color-mix(in srgb, black 28%, transparent),
+    0 0 0 1px var(--accent-lo),
+    0 12px 26px -14px var(--accent);
+  transition: transform .18s var(--ease), box-shadow .3s;
+}
+.btn-gloss.btn-gloss-round { border-radius: 50%; }
+.btn-gloss.btn-gloss-sm { width: 36px; height: 36px; }
+.btn-gloss svg { width: 18px; height: 18px; color: var(--on-accent); }
+.btn-gloss::before {
+  content: "";
+  position: absolute;
+  left: 0;
+  right: 0;
+  top: 0;
+  height: 50%;
+  background: linear-gradient(180deg, color-mix(in srgb, white 20%, transparent), transparent);
+  z-index: -1;
+}
+.btn-gloss::after {
+  content: "";
+  position: absolute;
+  top: -10%;
+  bottom: -10%;
+  width: 55%;
+  left: -90%;
+  background: linear-gradient(100deg, transparent, color-mix(in srgb, white 42%, transparent), transparent);
+  transform: skewX(-20deg);
+  transition: left .8s var(--ease);
+}
+.btn-gloss:hover::after,
+.btn-gloss:focus-visible::after { left: 140%; }
+.btn-gloss:active:not(:disabled) { transform: scale(.96); }
+/* Disabled keeps a solid face (no opacity) so the icon stays readable. */
+.btn-gloss:disabled {
+  opacity: 1;
+  cursor: not-allowed;
+  background: var(--tile-3);
+  color: var(--ink-2);
+  box-shadow: inset 0 0 0 1px var(--line-2);
+}
+.btn-gloss:disabled svg { color: var(--ink-2); }
+.btn-gloss:disabled::before,
+.btn-gloss:disabled::after { display: none; }
+
+/* Reduced motion: hover and press states still change color, but nothing moves. */
+@media (prefers-reduced-motion: reduce) {
+  .btn-flip,
+  .btn-flip *,
+  .btn-grow,
+  .btn-grow *,
+  .btn-sweep,
+  .btn-sweep::before,
+  .btn-depth,
+  .btn-depth *,
+  .btn-depth::before,
+  .btn-depth::after,
+  .btn-spark,
+  .btn-spark *,
+  .btn-spark::before,
+  .btn-spark::after,
+  .btn-gloss,
+  .btn-gloss::before,
+  .btn-gloss::after {
+    transition: none !important;
+    animation: none !important;
+  }
+  .btn-flip:active,
+  .btn-grow:active,
+  .btn-sweep:active,
+  .btn-spark:active,
+  .btn-gloss:active { transform: none !important; }
+  .btn-grow:hover .btn-grow-circle svg,
+  .btn-grow:focus-visible .btn-grow-circle svg,
+  .btn-spark:hover .btn-spark-plus,
+  .btn-spark:focus-visible .btn-spark-plus { transform: none !important; }
+  .btn-spark .btn-spark-pts { display: none; }
+  .btn-spark:hover .btn-spark-hex,
+  .btn-spark:focus-visible .btn-spark-hex { fill: var(--on-accent); }
+  .btn-gloss::after { display: none; }
+}
diff --git a/tests/buttons.test.ts b/tests/buttons.test.ts
new file mode 100644
index 0000000..4575047
--- /dev/null
+++ b/tests/buttons.test.ts
@@ -0,0 +1,160 @@
+import { describe, expect, it } from "vitest";
+import { readFileSync } from "node:fs";
+import path from "node:path";
+import { createElement } from "react";
+import { renderToStaticMarkup } from "react-dom/server";
+import {
+  DepthButton,
+  FlipButton,
+  GrowButton,
+  IconButton,
+  SendIcon,
+  SparkleButton,
+  SweepButton,
+  flipLabels,
+} from "@/components/Buttons";
+import { ButtonGallery } from "@/components/ButtonGallery";
+
+const html = (el: Parameters<typeof renderToStaticMarkup>[0]) => renderToStaticMarkup(el);
+const css = readFileSync(path.resolve(__dirname, "../src/styles/buttons.css"), "utf8");
+const globals = readFileSync(path.resolve(__dirname, "../src/app/globals.css"), "utf8");
+
+/** Body of the first rule whose selector list matches exactly. */
+function rule(selector: string): string {
+  const esc = selector.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+  const m = css.match(new RegExp(`(?:^|\\n|,)\\s*${esc}\\s*\\{([^}]*)\\}`));
+  if (!m) throw new Error(`no rule for ${selector}`);
+  return m[1];
+}
+
+describe("FlipButton states", () => {
+  it("ready: POST plus send icon, flips to PUBLISH with the icon", () => {
+    expect(flipLabels("ready")).toEqual({ front: "Post", back: "Publish", icon: true });
+    const out = html(createElement(FlipButton, { state: "ready" }));
+    expect(out).toContain('class="btn-flip"');
+    expect(out).not.toContain("disabled");
+    expect(out.match(/<svg/g)).toHaveLength(2);
+    expect(out).toMatch(/btn-flip-back" aria-hidden="true">Publish/);
+  });
+
+  it("disabled: native disabled, flips to WRITE FIRST, no icon", () => {
+    const out = html(createElement(FlipButton, { state: "disabled" }));
+    expect(out).toContain('disabled=""');
+    expect(out).toMatch(/btn-flip-front">Post</);
+    expect(out).toMatch(/btn-flip-back" aria-hidden="true">Write first</);
+    expect(out).not.toContain("<svg");
+  });
+
+  it("posting: POSTING, busy, no flip panel", () => {
+    const out = html(createElement(FlipButton, { state: "posting" }));
+    expect(out).toContain("btn-flip btn-flip-busy");
+    expect(out).toContain('aria-busy="true"');
+    expect(out).toMatch(/btn-flip-front">Posting</);
+    expect(out).not.toContain("btn-flip-back");
+  });
+
+  it("the disabled face is solid graphite and never faded", () => {
+    const disabled = rule(".btn-flip:disabled");
+    expect(disabled).toMatch(/opacity:\s*1/);
+    expect(disabled).toMatch(/background:\s*var\(--tile-3\)/);
+    expect(disabled).toMatch(/color:\s*var\(--ink-2\)/);
+    expect(css).not.toMatch(/\.btn-flip[^{]*\{[^}]*opacity:\s*0?\.\d/);
+  });
+
+  it("sets text color explicitly for every state, never by inheritance", () => {
+    expect(rule(".btn-flip")).toMatch(/color:\s*var\(--bg\)/);
+    expect(rule(".btn-flip .btn-flip-front")).toMatch(/color:\s*var\(--bg\)/);
+    expect(rule(".btn-flip .btn-flip-back")).toMatch(/color:\s*var\(--on-accent\)/);
+    expect(rule(".btn-flip:disabled .btn-flip-front")).toMatch(/color:\s*var\(--ink-2\)/);
+    expect(rule(".btn-flip:disabled .btn-flip-back")).toMatch(/color:\s*var\(--ink\)/);
+    expect(rule(".btn-flip.btn-flip-busy:disabled .btn-flip-front")).toMatch(/color:\s*var\(--bg\)/);
+    // Face and text never share a token in any state.
+    expect(rule(".btn-flip")).toMatch(/background:\s*var\(--ink\)/);
+    expect(rule(".btn-flip.btn-flip-busy:disabled")).toMatch(/background:\s*var\(--ink\)/);
+  });
+});
+
+describe("the other styles", () => {
+  it("GrowButton renders the crimson circle and the label", () => {
+    const out = html(createElement(GrowButton, { label: "3 new posts" }));
+    expect(out).toContain('class="btn-grow"');
+    expect(out).toContain("btn-grow-circle");
+    expect(out).toMatch(/btn-grow-text">3 new posts</);
+  });
+
+  it("SweepButton stays filled and pressed when selected", () => {
+    expect(html(createElement(SweepButton, { label: "Business", selected: true }))).toContain('class="btn-sweep btn-sweep-on" aria-pressed="true"');
+    expect(html(createElement(SweepButton, { label: "Media", selected: false }))).toContain('aria-pressed="false"');
+    expect(html(createElement(SweepButton, { label: "Cancel" }))).not.toContain("aria-pressed");
+  });
+
+  it("DepthButton renders label, sublabel and icon", () => {
+    const out = html(createElement(DepthButton, { label: "Trending", sublabel: "Hot now", icon: createElement(SendIcon) }));
+    expect(out).toContain("btn-depth-icon");
+    expect(out).toMatch(/btn-depth-label">Trending</);
+    expect(out).toMatch(/btn-depth-sub">Hot now</);
+  });
+
+  it("SparkleButton: sign in has the fold, hexagon and ten sparks; fab has a plus and a name", () => {
+    const signin = html(createElement(SparkleButton, { label: "Sign in", type: "submit" }));
+    expect(signin).toContain("btn-spark-fold");
+    expect(signin).toContain("btn-spark-hex");
+    expect(signin.match(/<i><\/i>/g)).toHaveLength(10);
+    expect(signin).toContain('type="submit"');
+    const fab = html(createElement(SparkleButton, { variant: "fab", label: "New post" }));
+    expect(fab).toContain('aria-label="New post"');
+    expect(fab).toContain("btn-spark btn-spark-fab");
+    expect(fab).not.toContain("btn-spark-fold");
+    expect(fab).toContain("btn-spark-plus");
+  });
+
+  it("IconButton is the glossy crimson button with an accessible name", () => {
+    const out = html(createElement(IconButton, { label: "Send comment", icon: createElement(SendIcon), shape: "round", size: "sm" }));
+    expect(out).toContain('class="btn-gloss btn-gloss-round btn-gloss-sm"');
+    expect(out).toContain('aria-label="Send comment"');
+    expect(rule(".btn-gloss:disabled")).toMatch(/opacity:\s*1/);
+  });
+});
+
+describe("button CSS rules", () => {
+  it("uses only .btn-* class selectors", () => {
+    const selectors = css.replace(/\/\*[\s\S]*?\*\//g, "").match(/\.[a-zA-Z][\w-]*/g) ?? [];
+    expect(selectors.filter((s) => !s.startsWith(".btn-"))).toEqual([]);
+  });
+
+  it("does not include the rejected liquid waves or 3D drop buttons", () => {
+    expect(css).not.toMatch(/wave|wv/i);
+  });
+
+  it("stops hover and press motion under prefers-reduced-motion", () => {
+    const block = css.slice(css.indexOf("@media (prefers-reduced-motion: reduce)"));
+    expect(block.length).toBeGreaterThan(0);
+    for (const cls of ["btn-flip", "btn-grow", "btn-sweep", "btn-depth", "btn-spark", "btn-gloss"]) {
+      expect(block).toContain(`.${cls}`);
+    }
+    expect(block).toMatch(/transition:\s*none !important/);
+    expect(block).toMatch(/animation:\s*none !important/);
+    expect(block).toMatch(/transform:\s*none !important/);
+  });
+
+  it("every theme defines the button tokens", () => {
+    for (const token of ["--shadow-btn", "--shadow-float", "--neu-d", "--neu-l"]) {
+      expect(globals.match(new RegExp(`${token}:`, "g"))).toHaveLength(2);
+    }
+    expect(globals).toContain("--on-accent:");
+  });
+});
+
+describe("ButtonGallery story", () => {
+  it("shows every style in both themes", () => {
+    for (const theme of ["dark", "light"] as const) {
+      const out = html(createElement(ButtonGallery, { theme }));
+      expect(out).toContain(`data-theme="${theme}"`);
+      for (const cls of ["btn-flip", "btn-flip-busy", "btn-grow", "btn-sweep-on", "btn-depth", "btn-spark-fold", "btn-spark-fab", "btn-gloss"]) {
+        expect(out).toContain(cls);
+      }
+      expect(out).toMatch(/Write first/);
+      expect(out).toMatch(/Posting/);
+    }
+  });
+});