:root {
  --ink: #0D1A28;
  --deep: #16293D;
  --night: #1F3A4D;
  --gold: #C6A667;
  --amber: #E3A65A;
  --paper: #F3EEE5;
  --fog: #93A7B4;
  --line: #2C4356;
  --wine: #6E2E3A;
  --moss: #7C9789;

  --font-display: "PingFang SC", "Hiragino Sans GB", "Source Han Sans SC", "Microsoft YaHei", sans-serif;
  --font-body: "Songti SC", "Noto Serif CJK SC", "SimSun", "PingFang SC", "Microsoft YaHei", serif;
  --font-mono: ui-monospace, "SFMono-Regular", Menlo, Consolas, "Courier New", monospace;

  --maxw: 1240px;
  --gutter: clamp(18px, 4vw, 56px);
  --header-h: 68px;
  --ease: cubic-bezier(0.2, 0.7, 0.3, 1);
}

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 16px);
}

body {
  margin: 0;
  background-color: var(--ink);
  color: var(--paper);
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.85;
  -webkit-font-smoothing: antialiased;
}

[hidden] {
  display: none !important;
}

h1,
h2,
h3 {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.01em;
  color: var(--paper);
}

h1 {
  font-size: clamp(32px, 4.4vw, 52px);
}

h2 {
  font-size: clamp(24px, 2.7vw, 34px);
}

h3 {
  font-size: clamp(18px, 1.6vw, 22px);
}

p {
  margin: 0;
}

ul,
ol {
  margin: 0;
  padding: 0;
}

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

a {
  color: inherit;
}

button {
  font: inherit;
}

::selection {
  background-color: var(--amber);
  color: var(--ink);
}

:focus-visible {
  outline: 2px solid var(--amber);
  outline-offset: 2px;
}

#main-content {
  display: block;
  scroll-margin-top: calc(var(--header-h) + 16px);
}

/* ---------- header ---------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: var(--ink);
  border-bottom: 1px solid var(--line);
}

.skip-link {
  position: absolute;
  left: 12px;
  top: -80px;
  z-index: 90;
  padding: 10px 18px;
  background-color: var(--amber);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.08em;
  text-decoration: none;
  transition: top 0.16s var(--ease);
}

.skip-link:focus {
  top: 10px;
}

.header-shell {
  display: flex;
  align-items: center;
  gap: clamp(12px, 2vw, 28px);
  max-width: var(--maxw);
  min-height: var(--header-h);
  margin: 0 auto;
  padding: 0 var(--gutter);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  flex: none;
  text-decoration: none;
}

.brand-mark {
  position: relative;
  flex: none;
  width: 26px;
  height: 26px;
  border: 1px solid var(--gold);
  background-color: var(--deep);
}

.brand-mark::after {
  content: "";
  position: absolute;
  inset: 5px;
  background: linear-gradient(135deg, var(--amber) 0 50%, var(--night) 50% 100%);
}

.brand-text {
  display: flex;
  flex-direction: column;
  gap: 1px;
}

.brand-name {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 16px;
  line-height: 1.2;
  letter-spacing: -0.01em;
  color: var(--paper);
}

.brand-sub {
  font-family: var(--font-mono);
  font-size: 10px;
  line-height: 1.2;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--gold);
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  background-color: transparent;
  border: 1px solid var(--line);
  color: var(--paper);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  cursor: pointer;
  transition: border-color 0.18s var(--ease), color 0.18s var(--ease);
}

.nav-toggle:hover {
  border-color: var(--gold);
  color: var(--amber);
}

.nav-toggle-bar {
  position: relative;
  display: block;
  flex: none;
  width: 16px;
  height: 9px;
}

.nav-toggle-bar::before,
.nav-toggle-bar::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  height: 1px;
  background-color: currentColor;
  transition: transform 0.2s var(--ease), top 0.2s var(--ease);
}

.nav-toggle-bar::before {
  top: 0;
}

.nav-toggle-bar::after {
  top: 8px;
}

.site-header[data-open] .nav-toggle-bar::before {
  top: 4px;
  transform: rotate(45deg);
}

.site-header[data-open] .nav-toggle-bar::after {
  top: 4px;
  transform: rotate(-45deg);
}

.nav-toggle-label {
  display: inline-block;
}

.site-nav {
  display: flex;
  overflow-x: auto;
  scrollbar-width: none;
}

.site-nav::-webkit-scrollbar {
  display: none;
}

.nav-list {
  display: flex;
  align-items: center;
  list-style: none;
}

.nav-item {
  display: flex;
}

.nav-item + .nav-item {
  border-left: 1px solid var(--line);
}

.nav-link {
  position: relative;
  display: inline-block;
  padding: 8px clamp(8px, 1.1vw, 16px);
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 500;
  color: var(--fog);
  text-decoration: none;
  white-space: nowrap;
  transition: color 0.18s var(--ease);
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1px;
  background-color: var(--gold);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.18s var(--ease);
}

.nav-link:hover,
.nav-link:focus-visible {
  color: var(--paper);
}

.nav-link:hover::after {
  transform: scaleX(1);
}

.nav-link[aria-current="page"] {
  color: var(--paper);
  font-weight: 700;
}

.nav-link[aria-current="page"]::after {
  transform: scaleX(1);
}

.header-tools {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-left: auto;
  flex: none;
}

.search-hint {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 9px;
  border: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  color: var(--fog);
}

.keycap {
  display: inline-grid;
  place-items: center;
  min-width: 16px;
  height: 16px;
  padding: 0 3px;
  background-color: var(--night);
  color: var(--amber);
  font-family: var(--font-mono);
  font-size: 10px;
  line-height: 1;
  border-radius: 0;
}

.search-hint-text {
  display: inline-block;
}

.status-pill {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 10px;
  border: 1px solid var(--line);
  color: var(--fog);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  text-decoration: none;
  white-space: nowrap;
  transition: border-color 0.18s var(--ease), color 0.18s var(--ease);
}

.status-pill:hover {
  border-color: var(--moss);
  color: var(--paper);
}

.status-dot {
  flex: none;
  width: 6px;
  height: 6px;
  background-color: var(--moss);
  border-radius: 0;
  box-shadow: 0 0 0 3px rgba(124, 151, 137, 0.16);
}

.status-text {
  display: inline-block;
}

/* ---------- footer ---------- */

.site-footer {
  margin-top: clamp(64px, 9vw, 140px);
  background-color: var(--deep);
  border-top: 1px solid var(--line);
  color: var(--fog);
}

.footer-shell {
  display: grid;
  grid-template-columns: minmax(220px, 1fr) minmax(0, 1.9fr);
  gap: clamp(28px, 4vw, 56px);
  max-width: var(--maxw);
  margin: 0 auto;
  padding: clamp(40px, 6vw, 76px) var(--gutter) 0;
}

.footer-brand {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 14px;
}

.footer-mark {
  position: relative;
  width: 30px;
  height: 30px;
  border: 1px solid var(--gold);
  background-color: var(--ink);
}

.footer-mark::after {
  content: "";
  position: absolute;
  inset: 6px;
  background: linear-gradient(135deg, var(--amber) 0 50%, var(--night) 50% 100%);
}

.footer-brand-name {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 20px;
  line-height: 1.25;
  letter-spacing: -0.01em;
  color: var(--paper);
}

.footer-brand-sub {
  max-width: 26ch;
  font-size: 13px;
  line-height: 1.75;
  color: var(--fog);
}

.footer-cta {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin-top: 4px;
  padding: 9px 16px;
  border: 1px solid var(--gold);
  color: var(--gold);
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.02em;
  text-decoration: none;
  transition: background-color 0.18s var(--ease), color 0.18s var(--ease), border-color 0.18s var(--ease);
}

.footer-cta:hover {
  background-color: var(--amber);
  border-color: var(--amber);
  color: var(--ink);
}

.footer-nav {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: clamp(20px, 3vw, 40px);
}

.footer-col {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.footer-col-title {
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--gold);
}

.footer-list {
  display: flex;
  flex-direction: column;
  gap: 9px;
  list-style: none;
}

.footer-link {
  font-family: var(--font-display);
  font-size: 14px;
  color: var(--fog);
  text-decoration: none;
  transition: color 0.18s var(--ease);
}

.footer-link:hover,
.footer-link:focus-visible {
  color: var(--amber);
}

.footer-contact {
  grid-column: 1 / -1;
  display: grid;
  gap: 8px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
}

.footer-contact-row {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 4px 14px;
  font-size: 14px;
}

.footer-contact-label {
  min-width: 68px;
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.16em;
  color: var(--gold);
}

.footer-contact-value {
  font-family: var(--font-mono);
  font-size: 13px;
  letter-spacing: 0.02em;
  color: var(--paper);
}

.footer-response {
  margin-top: 6px;
  max-width: 70ch;
  font-size: 13px;
  line-height: 1.8;
  color: var(--fog);
}

.footer-legal {
  grid-column: 1 / -1;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 8px 24px;
  margin-top: 24px;
  padding: 18px 0 30px;
  border-top: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  color: var(--fog);
}

.footer-legal-line,
.footer-note {
  margin: 0;
}

/* ---------- shared layout ---------- */

.wrap {
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
  padding-inline: var(--gutter);
}

.prose {
  max-width: 74ch;
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.85;
  color: var(--paper);
}

.prose h2 {
  margin-top: 1.9em;
  padding-top: 0.7em;
  border-top: 1px solid var(--line);
}

.prose h3 {
  margin-top: 1.6em;
  color: var(--paper);
}

.prose p,
.prose ul,
.prose ol {
  margin-top: 1.2em;
}

.prose ul,
.prose ol {
  padding-left: 1.3em;
}

.prose li + li {
  margin-top: 0.4em;
}

.prose a {
  color: var(--amber);
  text-decoration: none;
  border-bottom: 1px solid var(--line);
  transition: border-color 0.18s var(--ease);
}

.prose a:hover {
  border-bottom-color: var(--amber);
}

.grid {
  display: grid;
  gap: clamp(16px, 2vw, 24px);
}

.grid--2 {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.grid--3 {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.grid--4 {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

/* ---------- shared components ---------- */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 11px 20px;
  border: 1px solid var(--gold);
  border-radius: 0;
  background-color: transparent;
  color: var(--paper);
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 600;
  letter-spacing: 0.02em;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.18s var(--ease), color 0.18s var(--ease), border-color 0.18s var(--ease);
}

.btn:hover {
  background-color: var(--night);
  border-color: var(--amber);
}

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

.btn--primary:hover {
  background-color: var(--gold);
  border-color: var(--gold);
  color: var(--ink);
}

.btn--ghost {
  border-color: var(--line);
  color: var(--fog);
}

.btn--ghost:hover {
  background-color: transparent;
  border-color: var(--gold);
  color: var(--paper);
}

.breadcrumb {
  padding-block: 18px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--fog);
}

.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  list-style: none;
}

.breadcrumb-item {
  display: flex;
  align-items: center;
}

.breadcrumb-item + .breadcrumb-item::before {
  content: "/";
  margin-right: 8px;
  color: var(--line);
}

.breadcrumb-link {
  color: var(--fog);
  text-decoration: none;
  transition: color 0.18s var(--ease);
}

.breadcrumb-link:hover {
  color: var(--amber);
}

.breadcrumb-current {
  color: var(--paper);
}

.label {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 11px;
  line-height: 1.6;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--gold);
}

.chapter-no {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  color: var(--gold);
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  list-style: none;
}

.tag {
  display: inline-block;
  padding: 3px 9px;
  border: 1px solid var(--line);
  border-radius: 0;
  background-color: transparent;
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  color: var(--fog);
  text-decoration: none;
  cursor: pointer;
  transition: border-color 0.18s var(--ease), color 0.18s var(--ease);
}

.tag:hover {
  border-color: var(--gold);
  color: var(--paper);
}

.tag[aria-pressed="true"],
.tag--active {
  border-color: var(--amber);
  color: var(--amber);
}

.media {
  position: relative;
  overflow: hidden;
  border: 1px solid var(--line);
  background-color: var(--deep);
}

.media img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.media--wide {
  aspect-ratio: 21 / 9;
}

.media--16x9 {
  aspect-ratio: 16 / 9;
}

.media--4x3 {
  aspect-ratio: 4 / 3;
}

.media--1x1 {
  aspect-ratio: 1 / 1;
}

.media-frame {
  padding: 10px;
  border: 1px solid var(--line);
  background-color: var(--deep);
}

.media-caption {
  margin-top: 10px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--fog);
}

.toc {
  display: flex;
  flex-direction: column;
  gap: 4px;
  list-style: none;
}

.toc-link {
  display: block;
  padding: 6px 0 6px 12px;
  border-left: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--fog);
  text-decoration: none;
  transition: color 0.18s var(--ease), border-color 0.18s var(--ease);
}

.toc-link:hover {
  color: var(--paper);
}

.toc-link[aria-current="true"] {
  color: var(--amber);
  border-left-color: var(--amber);
}

/* ---------- scroll utilities ---------- */

.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 70;
  width: 100%;
  height: 2px;
  pointer-events: none;
}

.scroll-progress-bar {
  display: block;
  width: 0;
  height: 100%;
  background-color: var(--amber);
}

.to-top {
  position: fixed;
  right: clamp(16px, 3vw, 32px);
  bottom: clamp(16px, 3vw, 32px);
  z-index: 60;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  padding: 0;
  border: 1px solid var(--gold);
  border-radius: 0;
  background-color: var(--deep);
  color: var(--gold);
  cursor: pointer;
  opacity: 0;
  transform: translateY(10px);
  pointer-events: none;
  transition: opacity 0.16s var(--ease), transform 0.16s var(--ease), background-color 0.18s var(--ease), color 0.18s var(--ease);
}

.to-top::before {
  content: "";
  width: 8px;
  height: 8px;
  margin-top: 4px;
  border-left: 1px solid currentColor;
  border-top: 1px solid currentColor;
  transform: rotate(45deg);
}

.to-top[data-visible] {
  opacity: 1;
  transform: none;
  pointer-events: auto;
}

.to-top:hover {
  background-color: var(--amber);
  border-color: var(--amber);
  color: var(--ink);
}

/* ---------- responsive ---------- */

@media (max-width: 1080px) {
  .grid--4 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 900px) {
  .header-shell {
    flex-wrap: wrap;
    padding-block: 10px;
  }

  .nav-toggle {
    display: inline-flex;
    order: 2;
    margin-left: auto;
  }

  .header-tools {
    order: 3;
    margin-left: 10px;
  }

  .search-hint {
    display: none;
  }

  .status-pill {
    padding: 6px;
    border-color: transparent;
  }

  .status-text {
    display: none;
  }

  .site-nav {
    order: 4;
    flex-basis: 100%;
    display: none;
    overflow: visible;
    margin-top: 10px;
    border-top: 1px solid var(--line);
  }

  .site-header[data-open] .site-nav {
    display: block;
  }

  .nav-list {
    flex-direction: column;
    align-items: stretch;
  }

  .nav-item + .nav-item {
    border-left: 0;
    border-top: 1px solid var(--line);
  }

  .nav-link {
    display: block;
    padding: 12px 4px 12px 14px;
    font-size: 15px;
  }

  .nav-link::after {
    left: 0;
    right: auto;
    top: 6px;
    bottom: 6px;
    width: 1px;
    height: auto;
    transform: scaleY(0);
    transform-origin: top center;
  }

  .nav-link:hover::after,
  .nav-link[aria-current="page"]::after {
    transform: scaleY(1);
  }

  .footer-shell {
    grid-template-columns: minmax(0, 1fr);
  }

  .grid--3 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 640px) {
  body {
    font-size: 16px;
  }

  .brand-name {
    font-size: 15px;
  }

  .grid--2,
  .grid--3,
  .grid--4 {
    grid-template-columns: minmax(0, 1fr);
  }

  .footer-nav {
    grid-template-columns: minmax(0, 1fr);
    gap: 24px;
  }

  .footer-legal {
    flex-direction: column;
  }
}

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

  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }

  .to-top {
    transform: none;
  }
}