:root {
  --font-display: "Inter", "Noto Sans SC", "Noto Sans JP", "Noto Sans KR", system-ui, sans-serif;
  --font-body: "Inter", "Noto Sans SC", "Noto Sans JP", "Noto Sans KR", system-ui, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Consolas, monospace;

  --color-bg: #fbfcfc;
  --color-panel: #ffffff;
  --color-panel-soft: #f5faf9;
  --color-panel-tint: #edf8f7;
  --color-border: #dce8e5;
  --color-border-strong: #c8dcd7;
  --color-accent: #00a86b;
  --color-accent-dark: #087a57;
  --color-accent-soft: #dff5eb;
  --color-cyan: #27b7c6;
  --color-text: #17201e;
  --color-text-muted: #66736f;
  --color-text-soft: #87938f;
  --color-white: #ffffff;
  --color-success: #00a86b;
  --color-warn: #6d654a;
  --color-error: #7b4a4a;
  --color-dark-button: #17201e;
  --color-dark-button-hover: #26312e;
  --color-shadow: rgba(26, 67, 56, 0.1);
  --color-shadow-soft: rgba(35, 75, 65, 0.06);
  --color-grid: rgba(8, 122, 87, 0.055);
  --color-sheen: rgba(255, 255, 255, 0.92);
  --color-overlay: rgba(23, 32, 30, 0.32);
  --color-success-ring: rgba(0, 168, 107, 0.18);

  --flag-red: #d84a55;
  --flag-red-dark: #b92e3d;
  --flag-blue: #315d9c;
  --flag-blue-dark: #224b87;
  --flag-white: #ffffff;
  --flag-off-white: #f7f8f6;
  --flag-black: #202523;
  --flag-yellow: #e5ba4e;

  --radius-xs: 6px;
  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --radius-xl: 32px;
  --radius-pill: 999px;

  --shadow-card: 0 22px 52px var(--color-shadow);
  --shadow-float: 0 14px 32px var(--color-shadow-soft);
  --shadow-button: 0 10px 22px var(--color-success-ring);

  --page-width: 1240px;
  --reading-width: 768px;
  --header-height: 78px;
  --gutter: 32px;
  --section-space: 104px;
  --toc-top: 92px;
  --toc-offset: 158px;
  --transition-fast: 180ms ease;
  --transition-slow: 700ms cubic-bezier(0.22, 1, 0.36, 1);
}

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

html {
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-body);
  scroll-behavior: smooth;
  text-size-adjust: 100%;
}

html.nav-open {
  overflow: hidden;
}

body {
  min-width: 0;
  min-height: 100vh;
  margin: 0;
  overflow-x: clip;
  background:
    linear-gradient(var(--color-grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--color-grid) 1px, transparent 1px),
    var(--color-bg);
  background-size: 72px 72px;
  font-size: 16px;
  line-height: 1.72;
}

main,
section,
article,
aside,
header,
footer,
nav,
div {
  min-width: 0;
}

img,
svg,
video,
canvas {
  display: block;
  max-width: 100%;
}

img {
  height: auto;
}

button,
input,
select,
textarea {
  color: inherit;
  font: inherit;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

button {
  border: 0;
  cursor: pointer;
}

a {
  color: inherit;
  text-decoration: none;
}

p,
ul,
ol,
blockquote,
pre,
table {
  margin-top: 0;
}

p {
  color: var(--color-text-muted);
}

strong {
  color: var(--color-text);
  font-weight: 680;
}

code,
kbd,
samp {
  font-family: var(--font-mono);
}

:not(pre) > code {
  padding: 0.12em 0.38em;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xs);
  background: var(--color-panel-tint);
  overflow-wrap: anywhere;
}

pre {
  max-width: 100%;
  padding: 20px;
  overflow-x: auto;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-text);
  color: var(--color-white);
  line-height: 1.65;
  -webkit-overflow-scrolling: touch;
}

pre code {
  white-space: pre;
  overflow-wrap: normal;
}

hr {
  height: 1px;
  margin: 40px 0;
  border: 0;
  background: var(--color-border);
}

::selection {
  background: var(--color-accent-soft);
  color: var(--color-text);
}

:focus-visible {
  outline: 3px solid var(--color-success-ring);
  outline-offset: 3px;
}

.wrap {
  width: 100%;
  max-width: calc(var(--page-width) + (var(--gutter) * 2));
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.reading-wrap {
  width: 100%;
  max-width: calc(var(--reading-width) + (var(--gutter) * 2));
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.section {
  padding-top: var(--section-space);
  padding-bottom: var(--section-space);
  overflow-x: clip;
}

.section-tint {
  background: var(--color-panel-tint);
}

.section-heading {
  max-width: 760px;
  margin-bottom: 44px;
}

.kicker,
.eyebrow {
  width: fit-content;
  display: inline-flex;
  align-items: center;
  gap: 9px;
  min-height: 32px;
  margin: 0 0 18px;
  padding: 0 13px 0 10px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  background: var(--color-panel);
  color: var(--color-accent-dark);
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 650;
  letter-spacing: 0.015em;
  box-shadow: 0 7px 20px var(--color-shadow-soft);
}

.kicker-dot,
.status-dot {
  width: 7px;
  height: 7px;
  flex: 0 0 auto;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
}

h1,
h2,
h3,
h4 {
  margin-top: 0;
  color: var(--color-text);
  font-family: var(--font-display);
  text-wrap: balance;
}

h1,
.hero-title {
  max-width: 760px;
  margin-bottom: 0;
  font-size: clamp(52px, 5.1vw, 72px);
  font-weight: 770;
  letter-spacing: -0.02em;
  line-height: 1.1;
}

h2 {
  margin-bottom: 18px;
  font-size: clamp(34px, 4vw, 48px);
  font-weight: 740;
  letter-spacing: -0.018em;
  line-height: 1.16;
}

h3 {
  margin-bottom: 12px;
  font-size: clamp(22px, 2.3vw, 28px);
  font-weight: 710;
  line-height: 1.3;
}

h4 {
  margin-bottom: 8px;
  font-size: 18px;
  font-weight: 700;
}

.title-gradient {
  color: var(--color-accent);
  background: linear-gradient(96deg, var(--color-accent-dark), var(--color-accent) 53%, var(--color-cyan));
  background-clip: text;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.no-break {
  white-space: nowrap;
}

.lead {
  max-width: 680px;
  margin-bottom: 0;
  color: var(--color-text-muted);
  font-size: clamp(18px, 2vw, 21px);
  line-height: 1.72;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 13px;
}

.button {
  min-height: 48px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  padding: 0 22px;
  border: 1px solid transparent;
  border-radius: var(--radius-sm);
  font-size: 15px;
  font-weight: 690;
  line-height: 1.2;
  transition:
    transform var(--transition-fast),
    background-color var(--transition-fast),
    border-color var(--transition-fast),
    box-shadow var(--transition-fast);
}

.button-primary {
  background: var(--color-dark-button);
  color: var(--color-white);
  box-shadow: var(--shadow-button);
}

.button-primary:hover,
.button-primary:focus-visible {
  background: var(--color-dark-button-hover);
  box-shadow: 0 13px 28px var(--color-success-ring);
  transform: translateY(-2px);
}

.button-secondary {
  border-color: var(--color-border-strong);
  background: var(--color-panel);
  color: var(--color-text);
  box-shadow: 0 6px 16px var(--color-shadow-soft);
}

.button-secondary:hover,
.button-secondary:focus-visible {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-float);
  transform: translateY(-2px);
}

.button-quiet {
  border-color: var(--color-border);
  background: var(--color-panel-soft);
  color: var(--color-accent-dark);
}

.button:disabled,
.button[aria-disabled="true"] {
  cursor: not-allowed;
  opacity: 0.55;
  transform: none;
}

.button-arrow {
  width: 19px;
  height: 19px;
  display: grid;
  flex: 0 0 auto;
  place-items: center;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
  color: var(--color-white);
  font-size: 12px;
}

.badge,
.tag,
.fact-pill {
  max-width: 100%;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  min-height: 30px;
  padding: 0 11px;
  overflow: hidden;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  background: var(--color-panel-soft);
  color: var(--color-text-muted);
  font-size: 12px;
  font-weight: 620;
}

.badge-accent,
.tag-accent {
  border-color: var(--color-success-ring);
  background: var(--color-accent-soft);
  color: var(--color-accent-dark);
}

.panel,
.card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-panel);
  box-shadow: var(--shadow-float);
}

.panel {
  padding: clamp(22px, 3vw, 36px);
}

.card {
  padding: 24px;
  transition:
    transform var(--transition-fast),
    box-shadow var(--transition-fast);
}

.card:hover {
  box-shadow: var(--shadow-card);
  transform: translateY(-3px);
}

.reveal {
  transition:
    opacity var(--transition-slow),
    transform var(--transition-slow);
}

.reveal.pending {
  opacity: 0;
  transform: translateY(16px);
}

.reveal.shown {
  opacity: 1;
  transform: none;
}

.site-header {
  position: relative;
  z-index: 100;
  min-height: var(--header-height);
  border-bottom: 1px solid var(--color-border);
  background: var(--color-sheen);
  backdrop-filter: blur(18px);
}

.nav-shell {
  width: 100%;
  max-width: calc(var(--page-width) + (var(--gutter) * 2));
  min-height: var(--header-height);
  display: flex;
  align-items: center;
  gap: 28px;
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.brand {
  display: inline-flex;
  align-items: center;
  flex: 0 0 auto;
  gap: 11px;
  margin-right: auto;
}

.brand-logo {
  width: 36px;
  height: 36px;
  flex: 0 0 auto;
  border-radius: var(--radius-sm);
  box-shadow: 0 8px 18px var(--color-success-ring);
}

.brand-wording {
  display: inline-flex;
  align-items: baseline;
  gap: 8px;
  white-space: nowrap;
}

.brand-en {
  font-family: var(--font-display);
  font-size: 21px;
  font-weight: 760;
  letter-spacing: -0.02em;
}

.brand-zh {
  color: var(--color-text-muted);
  font-size: 13px;
  font-weight: 520;
}

.primary-nav {
  display: flex;
  align-items: center;
  gap: 25px;
  white-space: nowrap;
}

.primary-nav a {
  position: relative;
  padding: 28px 0 26px;
  color: var(--color-text-muted);
  font-size: 14px;
  font-weight: 540;
  transition: color var(--transition-fast);
}

.primary-nav a::after {
  position: absolute;
  right: 0;
  bottom: 18px;
  left: 0;
  height: 2px;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
  content: "";
  opacity: 0;
  transform: scaleX(0.35);
  transition:
    opacity var(--transition-fast),
    transform var(--transition-fast);
}

.primary-nav a:hover,
.primary-nav a:focus-visible,
.primary-nav a[aria-current="page"] {
  color: var(--color-text);
}

.primary-nav a:hover::after,
.primary-nav a:focus-visible::after,
.primary-nav a[aria-current="page"]::after {
  opacity: 1;
  transform: scaleX(1);
}

.header-tools {
  display: flex;
  align-items: center;
  flex: 0 0 auto;
  gap: 9px;
}

.language-picker {
  position: relative;
}

.language-button {
  min-height: 40px;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 0 10px;
  background: transparent;
  color: var(--color-text-muted);
  font-size: 13px;
  font-weight: 560;
}

.language-menu {
  position: absolute;
  top: calc(100% + 10px);
  right: 0;
  z-index: 130;
  width: 172px;
  display: none;
  padding: 7px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-panel);
  box-shadow: var(--shadow-card);
}

.language-picker.open .language-menu {
  display: grid;
}

.language-menu a {
  min-height: 42px;
  display: flex;
  align-items: center;
  width: 100%;
  padding: 0 11px;
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  font-size: 13px;
}

.language-menu a:hover,
.language-menu a[aria-current="true"] {
  background: var(--color-panel-tint);
  color: var(--color-accent-dark);
}

.login-button {
  min-width: 72px;
  min-height: 40px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0 17px;
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-pill);
  background: var(--color-panel);
  color: var(--color-text);
  font-size: 14px;
  font-weight: 660;
  box-shadow: 0 5px 14px var(--color-shadow-soft);
  transition:
    border-color var(--transition-fast),
    transform var(--transition-fast),
    box-shadow var(--transition-fast);
}

.login-button:hover,
.login-button:focus-visible {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-float);
  transform: translateY(-1px);
}

.menu-button {
  width: 44px;
  min-width: 44px;
  min-height: 44px;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 0;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-panel);
}

.menu-icon,
.menu-icon::before,
.menu-icon::after {
  width: 18px;
  height: 2px;
  display: block;
  border-radius: var(--radius-pill);
  background: var(--color-text);
  content: "";
  transition: transform var(--transition-fast);
}

.menu-icon {
  position: relative;
}

.menu-icon::before {
  position: absolute;
  top: -6px;
}

.menu-icon::after {
  position: absolute;
  top: 6px;
}

.menu-button[aria-expanded="true"] .menu-icon {
  background: transparent;
}

.menu-button[aria-expanded="true"] .menu-icon::before {
  top: 0;
  transform: rotate(45deg);
}

.menu-button[aria-expanded="true"] .menu-icon::after {
  top: 0;
  transform: rotate(-45deg);
}

.mobile-drawer {
  display: none;
}

.nav-veil {
  position: fixed;
  inset: var(--header-height) 0 0;
  z-index: 80;
  display: none;
  background: var(--color-overlay);
}

.nav-veil.open {
  display: block;
}

.site-footer {
  overflow-x: clip;
  border-top: 1px solid var(--color-border);
  background: var(--color-panel);
}

.footer-main {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr 1fr;
  gap: 56px;
  padding-top: 68px;
  padding-bottom: 52px;
}

.footer-brand p {
  max-width: 390px;
  margin: 18px 0 0;
}

.footer-title {
  margin-bottom: 16px;
  color: var(--color-text);
  font-size: 13px;
  font-weight: 720;
  letter-spacing: 0.07em;
}

.footer-links {
  display: grid;
  gap: 9px;
}

.footer-links a {
  width: fit-content;
  color: var(--color-text-muted);
  font-size: 14px;
  transition: color var(--transition-fast);
}

.footer-links a:hover {
  color: var(--color-accent-dark);
}

.footer-keywords,
.footer-languages {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.footer-keywords a,
.footer-languages a {
  max-width: 100%;
  padding: 6px 10px;
  overflow: hidden;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  color: var(--color-text-muted);
  font-size: 12px;
}

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding-top: 21px;
  padding-bottom: 24px;
  border-top: 1px solid var(--color-border);
  color: var(--color-text-soft);
  font-size: 12px;
}

.footer-legal {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
}

.prose {
  color: var(--color-text-muted);
}

.prose h2 {
  margin-top: 2.2em;
}

.prose h3 {
  margin-top: 1.8em;
}

.prose p,
.prose li {
  overflow-wrap: break-word;
}

.prose li + li {
  margin-top: 8px;
}

.prose a {
  color: var(--color-accent-dark);
  text-decoration: underline;
  text-decoration-color: var(--color-success-ring);
  text-underline-offset: 3px;
}

.prose blockquote {
  margin-inline: 0;
}

.prose ol {
  counter-reset: prose-step;
  padding-left: 0;
  list-style: none;
}

.prose ol > li {
  position: relative;
  min-height: 34px;
  padding-left: 46px;
  counter-increment: prose-step;
}

.prose ol > li::before {
  position: absolute;
  top: 0;
  left: 0;
  width: 30px;
  height: 30px;
  display: grid;
  place-items: center;
  border-radius: var(--radius-pill);
  background: var(--color-accent-soft);
  color: var(--color-accent-dark);
  content: counter(prose-step);
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 700;
}

body:has(.toc-tabs) section[id] {
  scroll-margin-top: var(--toc-offset);
}

@media (max-width: 1060px) {
  :root {
    --gutter: 24px;
  }

  .primary-nav {
    gap: 16px;
  }

  .primary-nav a {
    font-size: 13px;
  }

  .language-button .language-label {
    display: none;
  }
}

@media (max-width: 900px) {
  :root {
    --header-height: 68px;
    --toc-top: 78px;
    --toc-offset: 142px;
  }

  .primary-nav,
  .desktop-language {
    display: none;
  }

  .header-tools {
    margin-left: auto;
  }

  .menu-button {
    display: inline-flex;
  }

  .mobile-drawer {
    position: fixed;
    top: var(--header-height);
    right: 0;
    left: 0;
    z-index: 120;
    max-height: calc(100dvh - var(--header-height));
    display: none;
    padding: 10px var(--gutter) 20px;
    overflow-y: auto;
    border-bottom: 1px solid var(--color-border);
    background: var(--color-panel);
    box-shadow: var(--shadow-card);
    overscroll-behavior: contain;
  }

  .mobile-drawer.open {
    display: block;
  }

  .mobile-drawer a {
    min-height: 48px;
    display: flex;
    align-items: center;
    width: 100%;
    padding: 0 12px;
    border-bottom: 1px solid var(--color-border);
    color: var(--color-text-muted);
    font-size: 15px;
    font-weight: 570;
  }

  .mobile-drawer a[aria-current="page"],
  .mobile-drawer a:hover {
    color: var(--color-accent-dark);
  }

  .drawer-languages {
    margin-top: 12px;
  }

  .drawer-languages strong {
    display: block;
    padding: 8px 12px;
    color: var(--color-text-soft);
    font-size: 11px;
    letter-spacing: 0.08em;
  }

  .footer-main {
    grid-template-columns: 1fr 1fr;
  }

  .footer-brand {
    grid-column: 1 / -1;
  }
}

@media (max-width: 768px) {
  :root {
    --section-space: 72px;
  }

  h1,
  .hero-title {
    font-size: clamp(28px, 9.5vw, 40px);
    letter-spacing: -0.015em;
    line-height: 1.12;
  }

  h2 {
    font-size: clamp(29px, 8vw, 38px);
  }

  .lead {
    font-size: 17px;
  }

  .decorative-label,
  .decorative-watermark {
    display: none;
  }

  .tilt,
  [class*="tilt-"] {
    transform: none;
  }
}

@media (max-width: 640px) {
  :root {
    --gutter: 18px;
    --section-space: 62px;
  }

  body {
    background-size: 54px 54px;
  }

  .nav-shell {
    gap: 9px;
  }

  .brand-logo {
    width: 33px;
    height: 33px;
  }

  .brand-en {
    font-size: 18px;
  }

  .brand-zh {
    display: none;
  }

  .login-button {
    min-width: 62px;
    min-height: 40px;
    padding-inline: 13px;
  }

  .button-row {
    align-items: stretch;
  }

  .button-row .button {
    flex: 1 1 145px;
  }

  .card,
  .panel {
    padding: 20px;
  }

  .footer-main {
    grid-template-columns: 1fr;
    gap: 36px;
  }

  .footer-brand {
    grid-column: auto;
  }

  .footer-bottom {
    align-items: flex-start;
    flex-direction: column;
  }

  .tilt,
  [class*="tilt-"] {
    transform: none !important;
  }
}

@media (max-width: 360px) {
  :root {
    --gutter: 16px;
  }

  .brand-wording {
    gap: 0;
  }

  .login-button {
    min-width: 58px;
    padding-inline: 11px;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .reveal,
  .reveal.pending {
    opacity: 1;
    transform: none;
  }
}