/* ===========================
  TAIILY — Design System
  Pure Black & White
  =========================== */

@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@400;500;700&display=swap');

/* ===========================
  CSS Variables
  =========================== */
:root {
  --bg: #000000;
  --ink: #FFFFFF;
  --border: rgba(255,255,255,0.2);

  --font: 'PingFang SC', 'Alibaba PuHuiTi 3.0', 'Noto Sans CJK SC', -apple-system, sans-serif;

  --text-xs: 11px;
  --text-sm: 13px;
  --text-base: 15px;
  --text-lg: 17px;
  --text-xl: 20px;
  --text-2xl: 28px;
  --text-3xl: 42px;
  --text-hero: clamp(48px, 10vw, 80px);

  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-5: 40px;
  --space-6: 48px;
  --space-8: 64px;
  --space-12: 96px;

  --max-w: 900px;
  --nav-h: 60px;
  --radius: 2px;

  --ease: 200ms ease;
}

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* ===========================
  Page Transition
  =========================== */
body {
  font-family: var(--font);
  font-size: var(--text-base);
  line-height: 1.65;
  color: var(--ink);
  background: var(--bg);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  animation: pageIn 0.4s cubic-bezier(0.22, 1, 0.36, 1) both;
}

@keyframes pageIn {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* View Transitions (same-origin) */
@view-transition {
  navigation: auto;
}

::view-transition-old(root) {
  animation: 200ms ease-out both fade-out;
}

::view-transition-new(root) {
  animation: 300ms cubic-bezier(0.22, 1, 0.36, 1) both slide-in;
}

@keyframes fade-out {
  to { opacity: 0; }
}

@keyframes slide-in {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* ===========================
  Scroll Animations
  =========================== */
.js-reveal {
  opacity: 0;
  transform: translateY(36px);
  transition: opacity 0.75s cubic-bezier(0.25, 0.46, 0.45, 0.94),
              transform 0.75s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

.js-reveal.in-view {
  opacity: 1;
  transform: translateY(0);
}

.delay-1 { transition-delay: 0.07s; }
.delay-2 { transition-delay: 0.14s; }
.delay-3 { transition-delay: 0.21s; }
.delay-4 { transition-delay: 0.28s; }
.delay-5 { transition-delay: 0.35s; }

/* Native scroll-driven (Chrome) */
@supports (animation-timeline: view()) {
  .js-reveal {
    opacity: 0;
    transform: translateY(36px);
    animation: scrollReveal linear both;
    animation-timeline: view();
    animation-range: entry 0% entry 100%;
  }

  .js-reveal.in-view { opacity: unset; transform: unset; }

  @keyframes scrollReveal {
    from {
      opacity: 0;
      transform: translateY(36px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }

  .delay-1 { animation-range: entry 7% entry calc(7% + 7%); }
  .delay-2 { animation-range: entry 14% entry calc(14% + 7%); }
  .delay-3 { animation-range: entry 21% entry calc(21% + 7%); }
  .delay-4 { animation-range: entry 28% entry calc(28% + 7%); }
  .delay-5 { animation-range: entry 35% entry calc(35% + 7%); }
}

a { color: inherit; text-decoration: none; }
img, svg { display: block; max-width: 100%; }
button { font-family: inherit; cursor: pointer; border: none; background: none; }
input, textarea { font-family: inherit; font-size: inherit; }
ul, ol { list-style: none; }

/* ===========================
  Typography
  =========================== */
h1, h2, h3, h4 {
  font-weight: 500;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

/* ===========================
  Layout
  =========================== */
.container {
  width: 100%;
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--space-4);
}

.section { padding: var(--space-8) 0; }
.section-sm { padding: var(--space-6) 0; }

/* ===========================
  Navigation
  =========================== */
.nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--nav-h);
  background: rgba(0, 0, 0, 0.9);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  z-index: 1000;
}

.nav-inner {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-size: var(--text-sm);
  font-weight: 700;
  letter-spacing: -0.04em;
}

.nav-logo span {
  font-weight: 400;
  opacity: 0.4;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-5);
}

.nav-link {
  font-size: var(--text-sm);
  font-weight: 500;
  color: rgba(255,255,255,0.45);
  letter-spacing: 0.01em;
  transition: color var(--ease);
}

.nav-link:hover,
.nav-link.active {
  color: var(--ink);
}

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 28px;
  height: 28px;
  padding: 4px;
}

.nav-toggle span {
  display: block;
  width: 100%;
  height: 1px;
  background: var(--ink);
  transition: var(--ease);
}

.nav-mobile {
  display: none;
  position: fixed;
  top: var(--nav-h);
  left: 0; right: 0; bottom: 0;
  background: var(--bg);
  padding: var(--space-6) var(--space-4);
  z-index: 999;
}

.nav-mobile.open { display: flex; flex-direction: column; gap: var(--space-4); }
.nav-mobile .nav-link { font-size: 28px; font-weight: 500; color: rgba(255,255,255,0.45); }
.nav-mobile .nav-link:hover { color: var(--ink); }

@media (max-width: 768px) {
  .nav-links { display: none; }
  .nav-toggle { display: flex; }
}

/* ===========================
  Buttons
  =========================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 20px;
  font-size: var(--text-sm);
  font-weight: 600;
  letter-spacing: -0.01em;
  border-radius: var(--radius);
  transition: all var(--ease);
  cursor: pointer;
}

.btn-primary {
  background: var(--ink);
  color: var(--bg);
}

.btn-primary:hover {
  opacity: 0.85;
}

.btn-secondary {
  background: transparent;
  color: var(--ink);
  box-shadow: inset 0 0 0 1px var(--border);
}

.btn-secondary:hover {
  box-shadow: inset 0 0 0 1px rgba(255,255,255,0.5);
  color: var(--ink);
}

.btn:disabled { opacity: 0.3; cursor: not-allowed; }

/* ===========================
  Divider
  =========================== */
.divider {
  border: none;
  border-top: 1px solid var(--border);
}

/* ===========================
  Footer
  =========================== */
.footer {
  margin-top: auto;
  border-top: 1px solid var(--border);
  padding: var(--space-5) 0;
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
}

.footer-text { font-size: var(--text-xs); opacity: 0.4; }

.footer-links { display: flex; gap: var(--space-4); }

.footer-link { font-size: var(--text-xs); opacity: 0.4; transition: opacity var(--ease); }
.footer-link:hover { opacity: 1; }

@media (max-width: 768px) {
  .footer-inner { flex-direction: column; text-align: center; }
}

/* ===========================
  Hero
  =========================== */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding-top: var(--nav-h);
  position: relative;
  overflow: hidden;
}

.hero-content {
  max-width: 720px;
  padding: 0 var(--space-4);
  position: relative;
  z-index: 1;
}

.hero-label {
  display: inline-block;
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  opacity: 0.4;
  margin-bottom: var(--space-4);
}

.hero-title {
  font-size: var(--text-hero);
  font-weight: 400;
  letter-spacing: -0.03em;
  line-height: 1.0;
  margin-bottom: var(--space-5);
  overflow: hidden;
}

.hero-title .line {
  display: inline-block;
  opacity: 0;
  transform: translateY(32px);
  animation: fadeUp 0.7s cubic-bezier(0.25, 0.46, 0.45, 0.94) forwards;
}

.hero-title .line:nth-child(1) { animation-delay: 0.35s; }
.hero-title .line:nth-child(2) { animation-delay: 0.35s; margin-left: 0.4em; }

.hero-actions {
  display: flex;
  gap: var(--space-2);
  justify-content: center;
  flex-wrap: wrap;
  opacity: 0;
  transform: translateY(16px);
  animation: fadeUp 0.6s ease forwards 0.75s;
}

/* ===========================
  Scroll Animations
  =========================== */
.js-reveal {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.55s cubic-bezier(0.22, 1, 0.36, 1),
              transform 0.55s cubic-bezier(0.22, 1, 0.36, 1);
}

.js-reveal.in-view {
  opacity: 1;
  transform: translateY(0);
}

.delay-1 { transition-delay: 0.06s; }
.delay-2 { transition-delay: 0.12s; }
.delay-3 { transition-delay: 0.18s; }
.delay-4 { transition-delay: 0.24s; }
.delay-5 { transition-delay: 0.30s; }

/* Native scroll-driven (Chrome) */
@supports (animation-timeline: view()) {
  .js-reveal {
    opacity: 0;
    transform: translateY(24px);
    animation: scrollReveal linear both;
    animation-timeline: view();
    animation-range: entry 0% entry 100%;
  }

  .js-reveal.in-view { opacity: unset; transform: unset; }

  @keyframes scrollReveal {
    from {
      opacity: 0;
      transform: translateY(24px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }

  .delay-1 { animation-range: entry 6% entry calc(6% + 6%); }
  .delay-2 { animation-range: entry 12% entry calc(12% + 6%); }
  .delay-3 { animation-range: entry 18% entry calc(18% + 6%); }
  .delay-4 { animation-range: entry 24% entry calc(24% + 6%); }
  .delay-5 { animation-range: entry 30% entry calc(30% + 6%); }
}

/* ===========================
  Product Item Hover
  =========================== */
.product-item {
  display: grid;
  grid-template-columns: 2.5em 1fr auto;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-4) 0;
  border-bottom: 1px solid var(--border);
  text-decoration: none;
  color: inherit;
  transition: opacity 0.3s ease;
  position: relative;
}

.product-item::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 0;
  background: rgba(255,255,255,0.03);
  transition: width 0.4s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

.product-item:hover::before { width: 100%; }
.product-item:hover { opacity: 1; }
.product-item:hover .product-item-arrow {
  opacity: 0.6;
  transform: translateX(4px);
}

.product-item.disabled { opacity: 0.25; cursor: not-allowed; }
.product-item.disabled::before { display: none; }
.product-item.disabled:hover { opacity: 0.25; }
.product-item.disabled:hover .product-item-arrow { opacity: 0; transform: none; }

/* ===========================
  Keyframes
  =========================== */
@keyframes revealLine {
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeUp {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes drawLine {
  from { width: 0; }
  to { width: 100%; }
}

/* ===========================
  Section Header
  =========================== */
.section-header {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: var(--space-4);
  margin-bottom: var(--space-6);
  padding-bottom: var(--space-4);
  border-bottom: 1px solid var(--border);
}

.section-eyebrow {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  opacity: 0.4;
  margin-bottom: var(--space-1);
}

.section-title {
  font-size: var(--text-xl);
  font-weight: 500;
  letter-spacing: -0.02em;
  line-height: 1.3;
}

.section-title.large {
  font-size: var(--text-2xl);
}

/* ===========================
  Product List (line-based)
  =========================== */
.product-list {
  display: flex;
  flex-direction: column;
}

.product-item {
  display: grid;
  grid-template-columns: 2.5em 1fr auto;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-4) 0;
  border-bottom: 1px solid var(--border);
  text-decoration: none;
  color: inherit;
  transition: opacity var(--ease);
}

.product-item:first-child {
  border-top: 1px solid var(--border);
}

.product-item:hover {
  opacity: 0.65;
}

.product-item.disabled {
  opacity: 0.25;
  cursor: not-allowed;
}

.product-item.disabled::before { display: none; }

.product-item.disabled:hover {
  opacity: 0.25;
}

.product-item.disabled:hover .product-item-arrow {
  opacity: 0;
  transform: none;
}

.product-item.disabled:hover {
  opacity: 0.25;
}

.product-item-index {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.1em;
  opacity: 0.4;
}

.product-item-body {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.product-item-title {
  font-size: var(--text-base);
  font-weight: 600;
  letter-spacing: -0.01em;
}

.product-item-desc {
  font-size: var(--text-sm);
  opacity: 0.45;
  line-height: 1.55;
}

.product-item-arrow {
  opacity: 0.3;
  transition: opacity var(--ease), transform var(--ease);
}

.product-item:hover .product-item-arrow {
  opacity: 0.6;
  transform: translateX(3px);
}

.product-item-arrow svg {
  width: 16px;
  height: 16px;
  stroke: currentColor;
  stroke-width: 1.5;
  fill: none;
}

/* ===========================
  Philosophy (text only)
  =========================== */
.philosophy {
  max-width: 520px;
}

.philosophy-title {
  font-size: var(--text-2xl);
  font-weight: 400;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-3);
  font-style: italic;
  opacity: 0.85;
}

.philosophy-text {
  font-size: var(--text-sm);
  opacity: 0.45;
  line-height: 1.8;
  letter-spacing: 0.01em;
}

/* ===========================
  CTA
  =========================== */
.cta {
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  padding: var(--space-8) 0;
  text-align: center;
}

.cta-title {
  font-size: var(--text-xl);
  font-weight: 500;
  margin-bottom: var(--space-2);
}

.cta-text {
  font-size: var(--text-sm);
  opacity: 0.4;
  margin-bottom: var(--space-4);
}

/* ===========================
  Page Header
  =========================== */
.page-header {
  padding: calc(var(--nav-h) + var(--space-8)) 0 var(--space-8);
  border-bottom: 1px solid var(--border);
}

.page-title {
  font-size: var(--text-3xl);
  font-weight: 400;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-2);
}

.page-subtitle {
  font-size: var(--text-sm);
  opacity: 0.4;
}

/* ===========================
  About Page
  =========================== */
.about-section {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--border);
}

.about-section:first-of-type {
  border-top: 1px solid var(--border);
}

.about-label {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  opacity: 0.4;
  margin-bottom: var(--space-3);
}

.about-body {
  font-size: var(--text-sm);
  line-height: 1.8;
  opacity: 0.55;
}

.about-body p + p {
  margin-top: var(--space-2);
}

.about-body em {
  font-style: italic;
  opacity: 0.75;
}

.changelog {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  margin-top: var(--space-3);
}

.changelog-item {
  display: grid;
  grid-template-columns: 5em 1fr;
  gap: var(--space-3);
  align-items: baseline;
}

.changelog-date {
  font-size: var(--text-xs);
  font-weight: 600;
  opacity: 0.35;
  letter-spacing: 0.04em;
}

.changelog-content {
  font-size: var(--text-sm);
  opacity: 0.55;
  line-height: 1.6;
}

/* ===========================
  Feature Page
  =========================== */
.feature {
  padding: var(--space-8) 0;
  border-bottom: 1px solid var(--border);
}

.feature:last-child { border-bottom: none; }

.feature-inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-8);
  align-items: start;
}

.feature-meta {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  position: sticky;
  top: calc(var(--nav-h) + var(--space-4));
}

.feature-index {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  opacity: 0.3;
}

.feature-title {
  font-size: var(--text-2xl);
  font-weight: 500;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-2);
}

.feature-desc {
  font-size: var(--text-sm);
  opacity: 0.5;
  line-height: 1.75;
}

.feature-icon {
  width: 40px;
  height: 40px;
  margin-bottom: var(--space-2);
  opacity: 0.7;
}

.feature-icon svg {
  width: 100%;
  height: 100%;
  stroke: var(--ink);
  stroke-width: 1.2;
  fill: none;
}

.feature-detail {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: var(--space-4);
}

.feature-detail-title {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  opacity: 0.3;
  margin-bottom: var(--space-3);
}

.feature-detail-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.feature-detail-item {
  font-size: var(--text-sm);
  opacity: 0.55;
  padding-left: var(--space-3);
  border-left: 1px solid var(--border);
  line-height: 1.5;
}

@media (max-width: 768px) {
  .feature-inner {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }
  .feature-meta { position: static; }
  .section-header { flex-direction: column; align-items: flex-start; }
}

/* ===========================
  Message Page
  =========================== */
.message-form {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  max-width: 100%;
}

.message-note {
  font-size: var(--text-xs);
  opacity: 0.35;
  line-height: 1.6;
}

.form-group { display: flex; flex-direction: column; gap: 8px; }

.form-label {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.4;
}

.form-input,
.form-textarea {
  width: 100%;
  padding: 12px 14px;
  font-size: var(--text-base);
  color: var(--ink);
  background: transparent;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  transition: border-color var(--ease);
  outline: none;
}

.form-input:focus,
.form-textarea:focus {
  border-color: rgba(255,255,255,0.5);
}

.form-textarea { resize: vertical; min-height: 100px; line-height: 1.65; }

.form-input::placeholder,
.form-textarea::placeholder { opacity: 0.25; }

.form-success {
  padding: var(--space-3) var(--space-4);
  border: 1px solid rgba(255,255,255,0.2);
  border-radius: var(--radius);
  font-size: var(--text-sm);
  opacity: 0.6;
}

.form-error {
  padding: var(--space-3) var(--space-4);
  border: 1px solid rgba(255,80,80,0.3);
  border-radius: var(--radius);
  font-size: var(--text-sm);
  color: #FF6464;
  opacity: 0.8;
}

/* Message list items — compact */
.message-item {
  padding: var(--space-3) 0;
  border-bottom: 1px solid var(--border);
  animation: fadeUp 0.3s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.message-item:first-child {
  border-top: 1px solid var(--border);
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.message-item-meta {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-bottom: 6px;
}

.message-item-name {
  font-size: var(--text-sm);
  font-weight: 600;
  opacity: 0.7;
}

.message-item-date {
  font-size: var(--text-xs);
  opacity: 0.3;
}

.message-item-text {
  font-size: var(--text-sm);
  opacity: 0.55;
  line-height: 1.7;
}

/* ===========================
  Mobile overrides
  =========================== */
@media (max-width: 640px) {
  .product-item {
    grid-template-columns: 2em 1fr;
  }
  .product-item-arrow { display: none; }
  .hero-title { font-size: clamp(40px, 12vw, 64px); }
}