:root {
  --color-bg: #F4F5F7;
  --color-dark: #1A1F2E;
  --color-deepblue: #0F2B46;
  --color-orange: #FF6B35;
  --color-teal: #00D4AA;
  --color-violet: #7C5FBF;
  --color-gold: #C9A96A;
  --color-body: #4A5568;
  --color-white: #FFFFFF;
  --font-heading: "Noto Sans CJK SC", "Microsoft YaHei", "PingFang SC", sans-serif;
  --font-body: "Microsoft YaHei", "PingFang SC", "Segoe UI", sans-serif;
  --font-mono: "JetBrains Mono", "SFMono-Regular", Consolas, monospace;
  --max-header: 1440px;
  --max-content: 1200px;
  --space-lg: clamp(1rem, 4vw, 2.5rem);
}

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

html, body {
  margin: 0;
  padding: 0;
}

body {
  background: var(--color-bg);
  color: var(--color-body);
  font-family: var(--font-body);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  -webkit-font-smoothing: antialiased;
}

#main-content {
  flex: 1 0 auto;
}

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

ul, ol {
  margin: 0;
  padding: 0;
  list-style: none;
}

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

button {
  font: inherit;
  border: none;
  cursor: pointer;
  background: none;
  color: inherit;
}

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

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 3000;
  background: var(--color-orange);
  color: #fff;
  padding: 0.75rem 1.25rem;
  font-weight: 700;
  border-radius: 0 0 4px 0;
}

.skip-link:focus {
  left: 0;
}

.site-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: linear-gradient(90deg, var(--color-orange) 0 25%, var(--color-teal) 25% 55%, var(--color-deepblue) 55% 100%);
  transform: scaleX(0);
  transform-origin: 0 50%;
  z-index: 3001;
  pointer-events: none;
  will-change: transform;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: var(--color-white);
  border-bottom: 3px solid var(--color-deepblue);
  box-shadow: 0 2px 12px rgba(15, 43, 70, 0.06);
}

.masthead {
  max-width: var(--max-header);
  margin-inline: auto;
  padding: 1rem var(--space-lg) 0.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  border-bottom: 1px solid #E2E8F0;
}

.brand {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
}

.brand__name {
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 1.75rem;
  line-height: 1;
  color: var(--color-deepblue);
  letter-spacing: 0.02em;
}

.brand__sub {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-body);
  letter-spacing: 0.14em;
}

.masthead__feedback {
  background: var(--color-orange);
  color: #fff;
  font-weight: 700;
  font-size: 0.875rem;
  padding: 0.5rem 1.25rem;
  line-height: 1.2;
  clip-path: polygon(0 0, calc(100% - 8px) 0, 100% 8px, 100% 100%, 0 100%);
  transition: background 0.15s ease;
}

.masthead__feedback:hover {
  background: #D9501D;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: 0.5rem;
  border: 2px solid var(--color-deepblue);
  padding: 0.375rem 0.75rem;
  color: var(--color-deepblue);
  font-weight: 700;
  line-height: 1;
}

.nav-toggle__text {
  font-size: 0.875rem;
}

.nav-toggle__icon {
  display: inline-block;
  width: 18px;
  height: 2px;
  background: currentColor;
  position: relative;
}

.nav-toggle__icon::before,
.nav-toggle__icon::after {
  content: "";
  position: absolute;
  left: 0;
  width: 100%;
  height: 2px;
  background: currentColor;
}

.nav-toggle__icon::before {
  top: -6px;
}

.nav-toggle__icon::after {
  top: 6px;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__icon {
  background: transparent;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__icon::before {
  top: 0;
  transform: rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle__icon::after {
  top: 0;
  transform: rotate(-45deg);
}

.primary-nav {
  max-width: var(--max-header);
  margin-inline: auto;
  padding: 0.25rem var(--space-lg) 0.75rem;
}

.primary-nav__list {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: clamp(0.5rem, 2.5vw, 2.5rem);
}

.nav-link {
  position: relative;
  display: inline-block;
  padding: 0.5rem 0.25rem;
  color: var(--color-deepblue);
  font-weight: 700;
  font-size: 1rem;
  letter-spacing: 0.04em;
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -1px;
  width: 100%;
  height: 3px;
  background: var(--color-orange);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.15s ease;
}

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

.nav-link[aria-current="page"] {
  color: var(--color-orange);
}

.site-footer {
  background: var(--color-dark);
  color: #CBD5E1;
  margin-top: auto;
}

.site-footer::before {
  content: "";
  display: block;
  height: 4px;
  background: linear-gradient(90deg, var(--color-orange) 0 30%, var(--color-teal) 30% 60%, var(--color-deepblue) 60% 100%);
}

.footer-inner {
  max-width: var(--max-header);
  margin-inline: auto;
  padding: 3rem var(--space-lg) 1.5rem;
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 0.8fr 1.2fr;
  gap: 2rem;
  padding-bottom: 2rem;
}

.footer-brand__name {
  font-family: var(--font-heading);
  font-size: 1.75rem;
  font-weight: 800;
  color: #fff;
  display: block;
  line-height: 1.2;
}

.footer-brand__sub {
  color: var(--color-gold);
  font-weight: 600;
  letter-spacing: 0.12em;
  font-size: 0.875rem;
}

.footer-trust {
  margin-top: 0.875rem;
  color: #94A3B8;
  font-size: 0.875rem;
  line-height: 1.75;
}

.footer-links__title,
.footer-contact__title {
  color: #fff;
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.75rem;
}

.footer-links li + li,
.footer-contact li + li {
  margin-top: 0.5rem;
}

.footer-links a {
  color: #CBD5E1;
  transition: color 0.15s ease;
}

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

.footer-contact li {
  color: #CBD5E1;
}

.footer-contact li:nth-child(3) {
  color: #94A3B8;
}

.footer-feedback {
  margin-top: 0.75rem;
  font-size: 0.875rem;
  color: var(--color-teal);
}

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.5rem;
  border-top: 1px solid #2D3548;
  padding-top: 1rem;
  color: #64748B;
  font-size: 0.875rem;
}

.back-top {
  position: fixed;
  right: 1.25rem;
  bottom: 1.25rem;
  width: 2.75rem;
  height: 2.75rem;
  background: var(--color-deepblue);
  color: #fff;
  border-radius: 4px;
  display: grid;
  place-items: center;
  font-size: 1.25rem;
  line-height: 1;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
  opacity: 0;
  visibility: hidden;
  transform: translateY(0.5rem);
  transition: opacity 0.15s ease, transform 0.15s ease, background 0.15s ease;
  z-index: 1500;
}

.back-top[data-shown] {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-top:hover {
  background: var(--color-orange);
}

.container {
  max-width: var(--max-content);
  margin-inline: auto;
  padding-inline: var(--space-lg);
}

.split {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  gap: clamp(1.5rem, 4vw, 3rem);
}

.grid {
  display: grid;
  gap: 1.5rem;
}

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

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

.btn {
  display: inline-block;
  background: var(--color-orange);
  color: #fff;
  font-weight: 700;
  padding: 0.75rem 1.5rem;
  border: 0;
  line-height: 1.2;
  text-align: center;
  clip-path: polygon(0 0, calc(100% - 8px) 0, 100% 8px, 100% 100%, 0 100%);
  transition: background 0.15s ease, transform 0.15s ease;
}

.btn:hover {
  background: #D9501D;
  transform: translateY(-1px);
}

.btn--outline {
  background: transparent;
  color: var(--color-deepblue);
  box-shadow: inset 0 0 0 2px var(--color-deepblue);
  clip-path: none;
}

.btn--outline:hover {
  background: rgba(15, 43, 70, 0.06);
}

.btn--ghost {
  background: transparent;
  color: var(--color-deepblue);
  clip-path: none;
}

.btn--ghost:hover {
  background: rgba(15, 43, 70, 0.04);
}

.card {
  position: relative;
  background: var(--color-white);
  border: 1px solid #E2E8F0;
  padding: 1.5rem;
  box-shadow: 0 2px 8px rgba(15, 43, 70, 0.04);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.card::after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  width: 18px;
  height: 18px;
  background: linear-gradient(135deg, transparent 50%, var(--color-orange) 50%);
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 10px 24px rgba(15, 43, 70, 0.08);
}

.section-heading {
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: clamp(1.5rem, 2.5vw, 2.25rem);
  color: var(--color-deepblue);
  line-height: 1.2;
  margin-bottom: 1rem;
}

.section-heading[data-index]::before {
  content: attr(data-index);
  font-family: var(--font-mono);
  color: var(--color-orange);
  font-size: 0.8em;
  margin-right: 0.5rem;
  vertical-align: 0.08em;
}

.breadcrumb {
  font-size: 0.875rem;
  color: var(--color-body);
  margin-bottom: 2rem;
}

.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.breadcrumb li + li::before {
  content: "/";
  margin-right: 0.5rem;
  color: #CBD5E1;
}

.breadcrumb a {
  color: var(--color-deepblue);
  font-weight: 600;
}

.breadcrumb a:hover {
  color: var(--color-orange);
}

.breadcrumb [aria-current="page"] {
  color: var(--color-orange);
}

.toc {
  background: var(--color-white);
  border: 1px solid #E2E8F0;
  padding: 1.25rem;
  position: sticky;
  top: 5rem;
}

.toc__title {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--color-body);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 0.75rem;
}

.toc__list {
  border-left: 2px solid #E2E8F0;
}

.toc__link {
  display: block;
  padding: 0.375rem 0.75rem;
  margin-left: -2px;
  border-left: 2px solid transparent;
  color: var(--color-body);
  transition: color 0.15s, border-color 0.15s;
}

.toc__link:hover {
  color: var(--color-deepblue);
  border-left-color: var(--color-orange);
}

.toc__link[data-active] {
  color: var(--color-deepblue);
  border-left-color: var(--color-orange);
  font-weight: 700;
}

.metric {
  font-family: var(--font-mono);
  font-size: 1.125em;
  font-weight: 700;
  color: var(--color-deepblue);
  letter-spacing: -0.02em;
}

.tag {
  display: inline-block;
  background: rgba(0, 212, 170, 0.1);
  color: var(--color-deepblue);
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.25em 0.75em;
  border-radius: 999px;
  border: 1px solid rgba(0, 212, 170, 0.3);
}

.tag--orange {
  background: rgba(255, 107, 53, 0.1);
  color: var(--color-orange);
  border-color: rgba(255, 107, 53, 0.3);
}

.tag--violet {
  background: rgba(124, 95, 191, 0.1);
  color: var(--color-violet);
  border-color: rgba(124, 95, 191, 0.3);
}

@media (max-width: 768px) {
  .masthead__feedback {
    padding: 0.4rem 0.75rem;
    font-size: 0.75rem;
  }

  .nav-toggle {
    display: inline-flex;
  }

  .primary-nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    max-width: none;
    padding: 0.5rem var(--space-lg) 1rem;
    background: var(--color-white);
    border-top: 1px solid #E2E8F0;
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.08);
    display: none;
  }

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

  .primary-nav__list {
    flex-direction: column;
    gap: 0.25rem;
  }

  .nav-link {
    display: block;
    padding: 1rem 0.5rem;
    border-bottom: 1px solid #EEF0F3;
  }

  .nav-link::after {
    display: none;
  }

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

  .split,
  .grid--2,
  .grid--3 {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .brand__sub {
    display: none;
  }

  .brand__name {
    font-size: 1.4rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  html {
    scroll-behavior: auto;
  }

  .card:hover,
  .btn:hover {
    transform: none;
  }
}