/* === RESET & BASE === */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
html {
  scroll-behavior: smooth;
}
body {
  font-family: 'Inter', 'Roboto', sans-serif;
  background-color: #0A0A0A;
  color: #FFFFFF;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
ul, ol {
  list-style: none;
}
a {
  color: inherit;
  text-decoration: none;
}
img {
  display: block;
  max-width: 100%;
}
/* === CSS VARIABLES === */
:root {
  --color-primary: #DC143C;
  --color-primary-hover: #FF4500;
  --color-bg: #0A0A0A;
  --color-accent-gold: #FFD700;
  --color-accent-blue: #00BFFF;
  --color-surface: #1A1A1A;
  --color-text: #FFFFFF;
  --color-text-secondary: #B0B0B0;
  --color-border: #333333;
  --font-heading: 'Oswald', sans-serif;
  --font-body: 'Inter', sans-serif;
  --font-mono: 'Fira Code', monospace;
  --header-height: 70px;
  --container-padding: 20px;
}
/* === ACCESSIBILITY === */
:focus-visible {
  outline: 3px solid var(--color-accent-gold);
  outline-offset: 2px;
}
.skip-link {
  position: absolute;
  top: -100%;
  left: 0;
  z-index: 10000;
  padding: 8px 16px;
  background-color: var(--color-primary);
  color: var(--color-text);
  font-weight: 600;
}
.skip-link:focus {
  top: 0;
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
  html {
    scroll-behavior: auto;
  }
}
/* === CONTAINER & GRID === */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--container-padding);
}
.grid {
  display: grid;
  gap: 24px;
}
.grid--2 {
  grid-template-columns: repeat(2, 1fr);
}
.grid--3 {
  grid-template-columns: repeat(3, 1fr);
}
.grid--4 {
  grid-template-columns: repeat(4, 1fr);
}
@media (max-width: 1024px) {
  .grid--4 {
    grid-template-columns: repeat(2, 1fr);
  }
}
@media (max-width: 768px) {
  .grid--2, .grid--3, .grid--4 {
    grid-template-columns: 1fr;
  }
}
/* === PROGRESS BAR === */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 4px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent-gold));
  z-index: 9999;
  transition: width 0.1s linear;
}
/* === BUTTONS === */
.btn {
  display: inline-block;
  padding: 12px 32px;
  background-color: var(--color-primary);
  color: var(--color-text);
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 1rem;
  border: 2px solid transparent;
  cursor: pointer;
  transition: background-color 0.3s ease, border-color 0.3s ease;
  text-align: center;
}
.btn:hover {
  background-color: var(--color-primary-hover);
  border-color: var(--color-accent-gold);
}
/* === TAGS === */
.tag {
  display: inline-block;
  padding: 4px 12px;
  background-color: var(--color-surface);
  border: 1px solid var(--color-accent-gold);
  color: var(--color-accent-gold);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
}
/* === IMAGE CONTAINER === */
.img-container {
  background-color: var(--color-surface);
  background-size: cover;
  background-position: center;
  aspect-ratio: 16 / 9;
  border: 1px solid var(--color-border);
  overflow: hidden;
}
/* === SECTION / CHAPTER SYSTEM === */
.section {
  padding: 5rem 0;
}
.section__header {
  display: flex;
  align-items: baseline;
  gap: 16px;
  margin-bottom: 2.5rem;
  border-bottom: 2px solid var(--color-border);
  padding-bottom: 0.5rem;
}
.section__number {
  font-family: var(--font-heading);
  font-size: clamp(3rem, 6vw, 5rem);
  font-weight: 900;
  color: var(--color-primary);
  line-height: 1;
  opacity: 0.8;
}
/* === DATA CARD (通用数据块) === */
.data-card {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  padding: 24px;
  transition: border-color 0.3s ease, transform 0.3s ease;
}
.data-card:hover {
  border-color: var(--color-primary);
  transform: translateY(-4px);
}
.data-card__header {
  font-family: var(--font-heading);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 12px;
}
.data-card__stats {
  font-family: var(--font-mono);
  font-size: 2rem;
  font-weight: 700;
  color: var(--color-primary);
  display: flex;
  gap: 16px;
  margin-bottom: 12px;
}
.data-card__content {
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  line-height: 1.7;
}
/* === STUDY BOARD (专题研究板) === */
.study-board {
  display: grid;
  grid-template-areas:
    "summary terms"
    "evidence extended";
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  padding: 32px;
  background-color: var(--color-surface);
  border: 2px solid var(--color-border);
  position: relative;
}
.study-board::before {
  content: '';
  position: absolute;
  top: -6px;
  left: -6px;
  right: 6px;
  bottom: 6px;
  border: 1px solid var(--color-accent-gold);
  pointer-events: none;
}
.study-board__summary {
  grid-area: summary;
}
.study-board__evidence {
  grid-area: evidence;
}
.study-board__terms {
  grid-area: terms;
}
.study-board__extended {
  grid-area: extended;
}
.study-board__summary,
.study-board__evidence,
.study-board__terms,
.study-board__extended {
  padding: 16px;
  background-color: rgba(0,0,0,0.3);
  border-left: 4px solid var(--color-primary);
}
.study-board__summary::before { content: "📋 摘要"; display: block; font-weight: 700; color: var(--color-accent-gold); margin-bottom: 8px; }
.study-board__evidence::before { content: "📊 证据边界"; display: block; font-weight: 700; color: var(--color-accent-gold); margin-bottom: 8px; }
.study-board__terms::before { content: "📖 术语"; display: block; font-weight: 700; color: var(--color-accent-gold); margin-bottom: 8px; }
.study-board__extended::before { content: "🔗 延伸阅读"; display: block; font-weight: 700; color: var(--color-accent-gold); margin-bottom: 8px; }
@media (max-width: 768px) {
  .study-board {
    grid-template-areas:
      "summary"
      "evidence"
      "terms"
      "extended";
    grid-template-columns: 1fr;
    padding: 16px;
  }
}
/* === HEADER === */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background-color: transparent;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
  height: var(--header-height);
}
.header[data-scrolled] {
  background-color: rgba(10,10,10,0.95);
  box-shadow: 0 2px 20px rgba(0,0,0,0.5);
}
.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}
.header__brand {
  display: flex;
  align-items: center;
  gap: 16px;
}
.header__logo {
  font-family: var(--font-heading);
  font-weight: 900;
  font-size: 1.8rem;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 2px;
}
.header__tagline {
  display: none;
  color: var(--color-text-secondary);
  font-size: 0.8rem;
  letter-spacing: 1px;
}
@media (min-width: 768px) {
  .header__tagline {
    display: inline-block;
  }
}
/* === NAVIGATION === */
.header__nav-toggle {
  display: block;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
  z-index: 1100;
}
.header__nav-icon,
.header__nav-icon::before,
.header__nav-icon::after {
  display: block;
  width: 28px;
  height: 3px;
  background-color: var(--color-text);
  transition: transform 0.3s ease;
}
.header__nav-icon {
  position: relative;
}
.header__nav-icon::before,
.header__nav-icon::after {
  content: '';
  position: absolute;
  left: 0;
}
.header__nav-icon::before { top: -8px; }
.header__nav-icon::after { top: 8px; }
[data-nav-toggle][aria-expanded="true"] .header__nav-icon {
  background-color: transparent;
}
[data-nav-toggle][aria-expanded="true"] .header__nav-icon::before {
  transform: translateY(8px) rotate(45deg);
}
[data-nav-toggle][aria-expanded="true"] .header__nav-icon::after {
  transform: translateY(-8px) rotate(-45deg);
}
.header__nav {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  width: 300px;
  background-color: var(--color-bg);
  border-left: 2px solid var(--color-border);
  padding: 100px 32px 32px;
  transform: translateX(100%);
  transition: transform 0.3s ease;
  overflow-y: auto;
}
.header__nav[data-open] {
  transform: translateX(0);
}
.header__nav-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.header__nav-list a {
  display: block;
  padding: 12px 16px;
  font-family: var(--font-heading);
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  border-left: 3px solid transparent;
  transition: color 0.3s ease, border-color 0.3s ease, background-color 0.3s ease;
}
.header__nav-list a:hover {
  color: var(--color-primary);
  background-color: var(--color-surface);
}
.header__nav-list a[aria-current="page"] {
  color: var(--color-primary);
  border-left-color: var(--color-primary);
  background-color: var(--color-surface);
}
@media (min-width: 1024px) {
  .header__nav-toggle {
    display: none;
  }
  .header__nav {
    position: static;
    transform: none;
    background: none;
    border-left: none;
    padding: 0;
    width: auto;
    overflow: visible;
  }
  .header__nav-list {
    flex-direction: row;
    gap: 4px;
  }
  .header__nav-list a {
    font-size: 0.95rem;
    padding: 8px 16px;
    border-left: none;
    border-bottom: 2px solid transparent;
  }
  .header__nav-list a[aria-current="page"] {
    border-left: none;
    border-bottom-color: var(--color-primary);
  }
}
/* === FOOTER === */
.footer {
  background-color: #0A0A0A;
  border-top: 2px solid var(--color-border);
  padding: 4rem 0 0;
  margin-top: 4rem;
}
.footer__inner {
  display: grid;
  grid-template-columns: 1fr;
  gap: 32px;
}
@media (min-width: 768px) {
  .footer__inner {
    grid-template-columns: 1fr 1fr 1fr;
  }
}
.footer__brand {
  display: flex;
  flex-direction: column;
  gap: 16px;
}
.footer__logo {
  font-family: var(--font-heading);
  font-size: 2rem;
  font-weight: 900;
  color: var(--color-primary);
}
.footer__trust {
  color: var(--color-text-secondary);
  font-size: 0.85rem;
  line-height: 1.7;
}
.footer__links-title,
.footer__contact-title {
  display: block;
  font-family: var(--font-heading);
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-accent-gold);
  margin-bottom: 16px;
}
.footer__links {
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.footer__links a {
  color: var(--color-text-secondary);
  transition: color 0.3s ease, padding-left 0.3s ease;
  border-left: 2px solid transparent;
  padding-left: 8px;
}
.footer__links a:hover {
  color: var(--color-primary);
  border-left-color: var(--color-primary);
  padding-left: 16px;
}
.footer__contact p {
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  margin-bottom: 8px;
}
.footer__contact-note {
  color: var(--color-accent-blue) !important;
  font-size: 0.8rem !important;
  margin-top: 12px !important;
}
.footer__bottom {
  grid-column: 1 / -1;
  border-top: 1px solid var(--color-border);
  padding: 24px 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
  align-items: center;
  text-align: center;
  color: var(--color-text-secondary);
  font-size: 0.85rem;
}
@media (min-width: 768px) {
  .footer__bottom {
    flex-direction: row;
    justify-content: space-between;
  }
}
/* === SCROLL TOP === */
.scroll-top {
  position: fixed;
  bottom: 40px;
  right: 40px;
  z-index: 500;
  width: 48px;
  height: 48px;
  background-color: var(--color-primary);
  color: var(--color-text);
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity 0.3s ease, visibility 0.3s ease, transform 0.3s ease;
  display: flex;
  align-items: center;
  justify-content: center;
}
.scroll-top[data-visible] {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}
.scroll-top:hover {
  background-color: var(--color-primary-hover);
}