:root {
  --color-bg: #FAFAFA;
  --color-panel: #FFFFFF;
  --color-panel-soft: #F1F3F4;
  --color-border: #E4E7E8;
  --color-accent: #00B8D9;
  --color-accent-dark: #007F93;
  --color-success: #00C985;
  --color-warn: #F5A524;
  --color-error: #D94A68;
  --color-text: #17191B;
  --color-muted: #62686D;
  --color-subtle: #8B9195;
  --color-shadow: rgba(23, 25, 27, 0.12);
  --color-shadow-soft: rgba(23, 25, 27, 0.06);
  --color-accent-soft: rgba(0, 184, 217, 0.12);
  --color-success-soft: rgba(0, 201, 133, 0.12);
  --color-warn-soft: rgba(245, 165, 36, 0.16);
  --color-error-soft: rgba(217, 74, 104, 0.12);
  --color-white-soft: rgba(255, 255, 255, 0.78);
  --color-grid: rgba(23, 25, 27, 0.05);
  --color-bus-glow: rgba(0, 184, 217, 0.26);
  --color-overlay: rgba(23, 25, 27, 0.42);
  --color-focus: rgba(0, 127, 147, 0.28);
  --color-flag-red: #D94A68;
  --color-flag-red-deep: #C92F4D;
  --color-flag-blue: #275BA8;
  --color-flag-blue-deep: #1D4380;
  --color-flag-white: #FFFFFF;
  --color-flag-black: #17191B;
  --color-korea-blue: #3479C4;
  --gradient-brand: linear-gradient(120deg, var(--color-accent), var(--color-success));
  --gradient-brand-reverse: linear-gradient(120deg, var(--color-success), var(--color-accent));
  --gradient-backdrop: linear-gradient(180deg, var(--color-accent-soft), var(--color-success-soft));
  --gradient-current: linear-gradient(135deg, var(--color-warn), var(--color-error));
  --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;
  --radius-xs: 6px;
  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --radius-xl: 34px;
  --radius-pill: 999px;
  --shadow-card: 0 28px 70px var(--color-shadow), 0 5px 16px var(--color-shadow-soft);
  --shadow-panel: 0 16px 44px var(--color-shadow-soft);
  --shadow-button: 0 12px 30px var(--color-bus-glow);
  --page-width: 1320px;
  --reading-width: 48rem;
  --header-height: 88px;
  --gutter: clamp(16px, 4vw, 32px);
  --section-space: clamp(72px, 9vw, 132px);
  --toc-offset: 104px;
  --transition-fast: 180ms ease;
  --transition-slow: 560ms cubic-bezier(.2, .75, .25, 1);
}

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

html {
  min-width: 320px;
  scroll-behavior: smooth;
  background: var(--color-bg);
}

html.nav-open {
  overflow: hidden;
}

body {
  min-width: 320px;
  min-height: 100%;
  margin: 0;
  overflow-x: clip;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.7;
  text-rendering: optimizeLegibility;
}

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

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

img {
  height: auto;
}

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

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

button {
  border: 0;
  cursor: pointer;
}

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

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

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

ul,
ol {
  padding-inline-start: 1.35rem;
}

li::marker {
  color: var(--color-accent-dark);
}

hr {
  border: 0;
  border-top: 1px solid var(--color-border);
}

code,
kbd {
  border-radius: var(--radius-xs);
  background: var(--color-panel-soft);
  font-family: var(--font-mono);
  font-size: .88em;
  overflow-wrap: anywhere;
}

code {
  padding: .15em .35em;
}

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

pre code {
  padding: 0;
  background: transparent;
  color: inherit;
  overflow-wrap: normal;
}

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

:focus-visible {
  outline: 3px solid var(--color-focus);
  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-tight {
  padding-top: calc(var(--section-space) * .65);
  padding-bottom: calc(var(--section-space) * .65);
}

h1,
h2,
h3,
h4 {
  margin-top: 0;
  color: var(--color-text);
  font-family: var(--font-display);
  line-height: 1.15;
  text-wrap: balance;
}

h1 {
  font-size: clamp(52px, 5.25vw, 72px);
  font-weight: 900;
  letter-spacing: -.02em;
}

h2 {
  margin-bottom: 20px;
  font-size: clamp(34px, 4vw, 52px);
  font-weight: 880;
  letter-spacing: -.018em;
}

h3 {
  margin-bottom: 12px;
  font-size: clamp(22px, 2.3vw, 30px);
  font-weight: 820;
}

h4 {
  margin-bottom: 8px;
  font-size: 18px;
  font-weight: 800;
}

.title-lock {
  white-space: nowrap;
}

.eyebrow,
.badge {
  display: inline-flex;
  align-items: center;
  max-width: 100%;
  min-height: 32px;
  gap: 8px;
  padding: 0 12px;
  overflow: hidden;
  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: 11px;
  font-weight: 750;
  line-height: 1.2;
}

.eyebrow-dot,
.status-dot {
  width: 9px;
  height: 9px;
  flex: 0 0 auto;
  border-radius: var(--radius-pill);
  background: var(--color-success);
  box-shadow: 0 0 0 5px var(--color-success-soft);
}

.headline-accent {
  display: inline-block;
  background: var(--gradient-brand);
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
}

.lead {
  max-width: 760px;
  color: var(--color-muted);
  font-size: clamp(18px, 2vw, 22px);
  line-height: 1.7;
}

.lead strong {
  color: var(--color-text);
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px;
}

.button {
  min-height: 50px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  padding: 0 22px;
  border: 1px solid transparent;
  border-radius: var(--radius-pill);
  font-size: 15px;
  font-weight: 800;
  line-height: 1.2;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), background var(--transition-fast);
}

.button:hover {
  transform: translateY(-2px);
}

.button-primary {
  background: var(--color-text);
  color: var(--color-panel);
  box-shadow: var(--shadow-button);
}

.button-secondary {
  border-color: var(--color-border);
  background: var(--color-panel-soft);
  color: var(--color-text);
}

.button-accent {
  background: var(--gradient-brand);
  color: var(--color-panel);
}

.button-small {
  min-height: 42px;
  padding-inline: 17px;
  font-size: 14px;
}

.button[aria-disabled="true"],
.button:disabled {
  cursor: not-allowed;
  opacity: .48;
  transform: none;
}

.button-icon {
  width: 20px;
  height: 20px;
  display: grid;
  flex: 0 0 auto;
  place-items: center;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
  color: var(--color-panel);
}

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

.panel {
  padding: clamp(22px, 4vw, 42px);
  box-shadow: var(--shadow-panel);
}

.card {
  padding: 24px;
}

.surface-soft {
  background: var(--color-panel-soft);
}

.site-header {
  position: relative;
  z-index: 100;
  min-height: var(--header-height);
  border-bottom: 1px solid var(--color-border);
  background: var(--color-white-soft);
}

.header-inner {
  position: relative;
  z-index: 100;
  width: 100%;
  max-width: calc(var(--page-width) + (var(--gutter) * 2));
  min-height: var(--header-height);
  display: flex;
  align-items: center;
  gap: 22px;
  margin-inline: auto;
  padding-inline: var(--gutter);
}

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

.brand-logo {
  width: 39px;
  height: 39px;
  flex: 0 0 auto;
}

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

.brand-en {
  font-size: 20px;
  font-weight: 850;
  letter-spacing: -.02em;
}

.brand-zh {
  color: var(--color-muted);
  font-size: 13px;
  font-weight: 600;
}

.desktop-nav {
  align-self: stretch;
  display: flex;
  align-items: stretch;
  gap: 2px;
}

.nav-link {
  position: relative;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  padding-inline: 10px;
  color: var(--color-muted);
  font-size: 14px;
  font-weight: 680;
  white-space: nowrap;
}

.nav-link::after {
  position: absolute;
  right: 10px;
  bottom: -1px;
  left: 10px;
  height: 3px;
  border-radius: var(--radius-pill) var(--radius-pill) 0 0;
  background: var(--gradient-brand);
  content: "";
  opacity: 0;
  transform: scaleX(.45);
  transition: opacity var(--transition-fast), transform var(--transition-fast);
}

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

.nav-link:hover::after,
.nav-link.is-active::after {
  opacity: 1;
  transform: scaleX(1);
}

.header-tools {
  display: flex;
  flex: 0 0 auto;
  align-items: center;
  gap: 8px;
}

.language-menu {
  position: relative;
}

.language-trigger {
  min-height: 40px;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding-inline: 13px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  background: var(--color-panel);
  color: var(--color-muted);
  font-size: 12px;
  font-weight: 700;
}

.language-list {
  position: absolute;
  top: calc(100% + 10px);
  right: 0;
  width: 172px;
  display: none;
  padding: 8px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-panel);
  box-shadow: var(--shadow-card);
}

.language-menu.is-open .language-list {
  display: grid;
}

.language-list a {
  min-height: 42px;
  display: flex;
  align-items: center;
  padding-inline: 12px;
  border-radius: var(--radius-sm);
  color: var(--color-muted);
  font-size: 13px;
}

.language-list a:hover,
.language-list a.is-current {
  background: var(--color-panel-soft);
  color: var(--color-text);
}

.login-button {
  min-height: 42px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding-inline: 19px;
  border-radius: var(--radius-pill);
  background: var(--color-text);
  color: var(--color-panel);
  font-size: 14px;
  font-weight: 780;
  white-space: nowrap;
}

.menu-button {
  width: 44px;
  min-width: 44px;
  height: 44px;
  display: none;
  place-items: center;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  background: var(--color-panel);
}

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

.menu-lines {
  position: relative;
}

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

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

.mobile-nav {
  position: absolute;
  z-index: 110;
  top: 100%;
  right: 0;
  left: 0;
  display: none;
  max-height: calc(100dvh - var(--header-height));
  overflow-y: auto;
  overscroll-behavior: contain;
  padding: 12px var(--gutter) 22px;
  border-top: 1px solid var(--color-border);
  background: var(--color-panel);
}

.mobile-nav.is-open {
  display: block;
}

.mobile-nav a {
  width: 100%;
  min-height: 48px;
  display: flex;
  align-items: center;
  padding-inline: 14px;
  border-bottom: 1px solid var(--color-border);
  color: var(--color-muted);
  font-weight: 720;
}

.mobile-nav a.is-active {
  color: var(--color-accent-dark);
}

.mobile-language {
  margin-top: 12px;
  border-top: 1px solid var(--color-border);
}

.nav-veil {
  position: fixed;
  z-index: 90;
  inset: var(--header-height) 0 0;
  display: none;
  background: var(--color-overlay);
}

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

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

.footer-grid {
  display: grid;
  grid-template-columns: 1.25fr 1fr 1.3fr .9fr;
  gap: 42px;
  padding-top: 70px;
  padding-bottom: 58px;
}

.footer-brand p {
  max-width: 360px;
  margin-top: 18px;
}

.footer-heading {
  margin-bottom: 16px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .08em;
  text-transform: uppercase;
}

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

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

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

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

.footer-keywords a {
  max-width: 100%;
  padding: 6px 10px;
  overflow: hidden;
  border-radius: var(--radius-pill);
  background: var(--color-panel-soft);
  color: var(--color-muted);
  font-size: 12px;
}

.footer-bottom {
  min-height: 66px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  border-top: 1px solid var(--color-border);
  color: var(--color-muted);
  font-size: 13px;
}

.footer-legal {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
}

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

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

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

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

.prose h2 {
  margin-top: 2.6em;
}

.prose h3 {
  margin-top: 2em;
}

.prose p,
.prose li {
  line-height: 1.85;
}

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

@media (max-width: 1180px) {
  .header-inner {
    gap: 12px;
  }

  .desktop-nav .nav-link {
    padding-inline: 7px;
    font-size: 12px;
  }

  .brand-zh,
  .language-trigger span {
    display: none;
  }

  .footer-grid {
    grid-template-columns: 1.3fr 1fr 1fr;
  }

  .footer-grid > :last-child {
    grid-column: 2 / -1;
  }
}

@media (max-width: 900px) {
  :root {
    --header-height: 72px;
  }

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

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

  .brand {
    margin-right: 0;
  }

  .menu-button {
    display: grid;
  }

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

  .footer-grid > :last-child {
    grid-column: auto;
  }
}

@media (max-width: 768px) {
  h1 {
    font-size: clamp(28px, 10vw, 40px);
    line-height: 1.12;
  }

  h2 {
    font-size: clamp(28px, 8vw, 38px);
  }

  .section {
    padding-top: 72px;
    padding-bottom: 72px;
  }

  .button-row .button {
    flex: 1 1 auto;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 34px;
  }

  .footer-bottom {
    align-items: flex-start;
    flex-direction: column;
    padding-top: 20px;
    padding-bottom: 20px;
  }

  .decorative-label {
    display: none;
  }
}

@media (max-width: 640px) {
  .wrap,
  .reading-wrap,
  .header-inner {
    padding-inline: max(16px, var(--gutter));
  }

  .brand-copy {
    gap: 0;
  }

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

  .brand-zh {
    display: none;
  }

  .login-button {
    min-height: 40px;
    padding-inline: 14px;
    font-size: 13px;
  }

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

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

  .button {
    min-height: 48px;
  }
}

@media (max-width: 390px) {
  .brand-logo {
    width: 34px;
    height: 34px;
  }

  .login-button {
    padding-inline: 12px;
  }

  .header-inner {
    gap: 7px;
  }
}

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

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

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