*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --color-primary: #0A1F3F;
  --color-secondary: #FF6B35;
  --color-card: #122A4A;
  --color-text: #FFFFFF;
  --color-text-muted: #B0B8C4;
  --color-bg-light: #F0F2F5;
  --color-text-dark: #333333;
  --gradient-orange: linear-gradient(135deg, #FF6B35, #FF8C5A);
  --glass-bg: rgba(10,31,63,0.7);
  --font-heading: "Montserrat Black", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial Black, sans-serif;
  --font-body: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial, sans-serif;
  --font-number: "Courier New", Courier, monospace;
  --spacing-unit: 1rem;
  --max-width: 1200px;
  --header-height: 64px;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  line-height: 1.6;
  color: var(--color-text);
  background-color: var(--color-primary);
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 900;
  line-height: 1.1;
  color: var(--color-text);
}

h1 { font-size: 6rem; }
h2 { font-size: 3.5rem; }
h3 { font-size: 2rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

p { margin-bottom: 1rem; }

a {
  color: var(--color-secondary);
  text-decoration: none;
  transition: color 0.2s, opacity 0.2s;
}

a:hover,
a:focus-visible {
  color: var(--color-secondary);
  opacity: 0.85;
}

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

ul { list-style: none; }

/* Skip Link */
.skip-link {
  position: absolute;
  top: -100%;
  left: 0;
  z-index: 10000;
  padding: 0.5rem 1rem;
  background: var(--color-secondary);
  color: var(--color-text);
  font-weight: bold;
  transition: top 0.2s;
}

.skip-link:focus-visible {
  top: 0;
}

/* Header */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  height: var(--header-height);
  background: var(--glass-bg);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1rem;
  height: 100%;
}

.header__brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.header__logo {
  font-family: var(--font-heading);
  font-size: 1.5rem;
  color: var(--color-text);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.header__nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  flex-direction: column;
  gap: 5px;
  padding: 0.5rem;
  margin-left: auto;
}

.header__nav-icon {
  display: block;
  width: 24px;
  height: 3px;
  background: var(--color-text);
  border-radius: 2px;
  transition: transform 0.2s, opacity 0.2s;
}

/* Sidebar Nav (desktop) */
.sidebar-nav {
  display: flex;
  align-items: center;
}

.sidebar-nav__list {
  display: flex;
  gap: 1.5rem;
  align-items: center;
}

.sidebar-nav a {
  font-family: var(--font-body);
  font-weight: 500;
  color: var(--color-text);
  padding: 0.5rem 0;
  position: relative;
  transition: color 0.2s, transform 0.2s;
}

.sidebar-nav a:hover,
.sidebar-nav a:focus-visible {
  color: var(--color-secondary);
  transform: scale(1.05);
}

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

.sidebar-nav a[aria-current="page"]::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--gradient-orange);
  border-radius: 2px;
}

/* Progress Bar */
.progress-bar {
  position: fixed;
  top: var(--header-height);
  left: 0;
  width: 0%;
  height: 4px;
  background: var(--gradient-orange);
  z-index: 999;
  transition: width 0.1s linear;
}

/* Footer */
.footer {
  background-color: var(--color-primary);
  border-top: 2px solid var(--color-secondary);
  padding: 3rem 1rem 1.5rem;
  margin-top: 4rem;
}

.footer__inner {
  max-width: var(--max-width);
  margin: 0 auto;
}

.footer__brand {
  margin-bottom: 2rem;
}

.footer__logo {
  font-family: var(--font-heading);
  font-size: 2rem;
  color: var(--color-text);
}

.footer__slogan {
  font-family: var(--font-heading);
  color: var(--color-secondary);
  font-size: 1.25rem;
  margin-top: 0.5rem;
}

.footer__columns {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2rem;
}

.footer__col-title {
  font-family: var(--font-heading);
  font-size: 1rem;
  color: var(--color-secondary);
  margin-bottom: 1rem;
  text-transform: uppercase;
}

.footer__list li {
  margin-bottom: 0.5rem;
  font-size: 0.875rem;
  color: var(--color-text-muted);
}

.footer__list a {
  color: var(--color-text);
  transition: color 0.2s;
}

.footer__list a:hover,
.footer__list a:focus-visible {
  color: var(--color-secondary);
}

.footer__bottom {
  margin-top: 2rem;
  text-align: center;
  font-size: 0.75rem;
  color: var(--color-text-muted);
  border-top: 1px solid rgba(255,255,255,0.1);
  padding-top: 1rem;
}

/* Button */
.btn {
  display: inline-block;
  padding: 0.75rem 1.5rem;
  background: var(--gradient-orange);
  border: none;
  border-radius: 4px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 1rem;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
  text-decoration: none;
  line-height: 1;
}

.btn:hover,
.btn:focus-visible {
  transform: scale(1.05);
  box-shadow: 0 4px 12px rgba(255,107,53,0.5);
}

/* Card */
.card {
  background-color: var(--color-card);
  border-radius: 12px;
  padding: 1.5rem;
  transition: transform 0.2s, box-shadow 0.2s;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 20px rgba(0,0,0,0.4);
}

/* Content Grid */
.content-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
}

/* Section */
.section {
  padding: 2rem 0;
}

/* Hero */
.hero {
  min-height: 80vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  padding: calc(var(--header-height) + 2rem) 1rem 2rem;
  position: relative;
  overflow: hidden;
}

.hero__title {
  font-size: 6rem;
  line-height: 1;
  margin-bottom: 0.5rem;
}

.hero__subtitle {
  font-size: 1.5rem;
  color: var(--color-text-muted);
  margin-bottom: 2rem;
  max-width: 600px;
}

.hero__index {
  display: flex;
  gap: 2rem;
  flex-wrap: wrap;
}

.hero__index a {
  font-family: var(--font-body);
  font-weight: 700;
  color: var(--color-secondary);
  padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
  transition: border-color 0.2s;
}

.hero__index a:hover,
.hero__index a:focus-visible {
  border-bottom-color: var(--color-secondary);
}

/* Split background (斜线装饰) */
.split-bg {
  background: linear-gradient(135deg, var(--color-primary) 50%, var(--color-card) 50%);
  clip-path: polygon(0 0, 100% 0, 100% 100%, 0 85%);
  position: absolute;
  inset: 0;
  z-index: -1;
}

/* Stat Number */
.stat-number {
  font-family: var(--font-number);
  font-size: 3.5rem;
  font-weight: bold;
  color: var(--color-secondary);
  line-height: 1;
}

/* Responsive */
@media (max-width: 768px) {
  :root {
    --header-height: 56px;
  }

  h1 { font-size: 3rem; }
  h2 { font-size: 2rem; }
  h3 { font-size: 1.5rem; }

  .header__nav-toggle {
    display: flex;
  }

  .sidebar-nav {
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    bottom: 0;
    background: var(--color-primary);
    flex-direction: column;
    align-items: center;
    justify-content: center;
    transform: translateX(100%);
    transition: transform 0.3s ease;
    z-index: 1001;
  }

  .sidebar-nav[data-open] {
    transform: translateX(0);
  }

  .sidebar-nav__list {
    flex-direction: column;
    gap: 2rem;
    text-align: center;
  }

  .sidebar-nav a {
    font-size: 1.5rem;
  }

  .footer__columns {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

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

  .hero__title {
    font-size: 3rem;
  }
}

@media (max-width: 480px) {
  .hero__title {
    font-size: 2.5rem;
  }
}

/* Focus visible */
:focus-visible {
  outline: 2px solid var(--color-secondary);
  outline-offset: 2px;
}

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

  .sidebar-nav {
    transition: none !important;
  }

  .progress-bar {
    transition: none !important;
  }
}