/* ===== Reset & Base ===== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  background: var(--color-bg-primary);
}

body {
  font-family: var(--font-body);
  background: var(--color-bg-primary);
  color: var(--color-text-primary);
  line-height: 1.6;
  min-height: 100vh;
  padding-top: var(--header-height);
}

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

button {
  font-family: inherit;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-title);
  line-height: 1.2;
  font-weight: 600;
}

a {
  color: var(--color-gold);
}

/* ===== CSS Variables ===== */
:root {
  --color-bg-primary: #0B1B3A;
  --color-bg-secondary: #102A5C;
  --color-bg-card: #1A2A4A;
  --color-bg-footer: #16213E;
  --color-gold: #D4AF37;
  --color-gold-light: #F0E68C;
  --color-neon-purple: #8A2BE2;
  --color-text-primary: #FFFFFF;
  --color-text-secondary: #B0B8C8;
  --color-border: rgba(212, 175, 55, 0.25);
  --color-border-strong: rgba(212, 175, 55, 0.6);

  --font-title: 'Oswald', 'Roboto Condensed', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-body: 'Fira Sans', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-mono: 'Orbitron', 'Courier New', monospace;

  --header-height: 72px;
  --container-width: 1200px;
  --space-unit: 8px;
  --transition-base: 0.2s ease;
}

/* ===== Utility ===== */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}

.container {
  width: min(100% - 48px, var(--container-width));
  margin-inline: auto;
}

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

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

/* ===== Buttons ===== */
.btn {
  display: inline-block;
  padding: 12px 24px;
  font-family: var(--font-title);
  font-size: 0.95rem;
  font-weight: 500;
  text-decoration: none;
  border: 1px solid transparent;
  background: transparent;
  cursor: pointer;
  transition: transform var(--transition-base), box-shadow var(--transition-base), background-color var(--transition-base), color var(--transition-base);
}

.btn-gold {
  background: linear-gradient(135deg, var(--color-gold), var(--color-gold-light));
  color: var(--color-bg-primary);
  border-color: var(--color-gold);
}

.btn-gold:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 20px rgba(212, 175, 55, 0.4);
}

.btn-outline {
  border-color: var(--color-border-strong);
  color: var(--color-gold);
}

.btn-outline:hover {
  background: rgba(212, 175, 55, 0.1);
}

/* ===== Skip Link ===== */
.skip-link {
  position: fixed;
  top: -48px;
  left: 8px;
  z-index: 2000;
  background: var(--color-gold);
  color: var(--color-bg-primary);
  padding: 8px 16px;
  font-weight: 700;
  text-decoration: none;
  transition: top var(--transition-base);
}

.skip-link:focus {
  top: 8px;
}

/* ===== Site Header ===== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: transparent;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

.site-header.is-scrolled {
  background: rgba(11, 27, 58, 0.95);
  box-shadow: 0 2px 24px rgba(0, 0, 0, 0.45);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: var(--header-height);
  gap: 16px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--color-text-primary);
}

.brand-mark {
  width: 36px;
  height: 36px;
  background: linear-gradient(135deg, var(--color-gold), var(--color-gold-light));
  color: var(--color-bg-primary);
  font-family: var(--font-title);
  font-weight: 700;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  clip-path: polygon(0 0, 100% 0, 100% 70%, 70% 100%, 0 100%);
  flex-shrink: 0;
}

.brand-text {
  font-family: var(--font-title);
  font-size: 1.4rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  color: inherit;
  transition: color var(--transition-base);
}

.brand:hover .brand-text {
  color: var(--color-gold);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 24px;
}

.nav-links a {
  color: var(--color-text-primary);
  text-decoration: none;
  font-size: 0.95rem;
  padding: 8px 4px;
  position: relative;
  opacity: 0.88;
  transition: opacity var(--transition-base);
}

.nav-links a::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-gold), var(--color-neon-purple));
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.25s ease;
}

.nav-links a:hover,
.nav-links a[aria-current="page"] {
  opacity: 1;
}

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

.header-cta {
  margin-left: 8px;
}

.nav-cta-mobile {
  display: none;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 6px;
}

.nav-toggle-bar {
  width: 24px;
  height: 2px;
  background: var(--color-gold);
  transition: transform 0.3s ease, opacity 0.3s ease;
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(2) {
  opacity: 0;
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ===== Scroll Progress ===== */
.scroll-progress {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  z-index: 1001;
  background: transparent;
}

.scroll-progress-bar {
  display: block;
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--color-gold), var(--color-neon-purple));
}

/* ===== Back to Top ===== */
.back-to-top {
  position: fixed;
  bottom: 28px;
  right: 28px;
  width: 46px;
  height: 46px;
  background: linear-gradient(135deg, var(--color-gold), var(--color-gold-light));
  color: var(--color-bg-primary);
  border: none;
  cursor: pointer;
  font-size: 1.4rem;
  line-height: 1;
  z-index: 1001;
  clip-path: polygon(0 0, 100% 0, 100% 78%, 50% 100%, 0 78%);
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity var(--transition-base), transform var(--transition-base), visibility var(--transition-base);
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--color-gold-light);
}

/* ===== Site Footer ===== */
.site-footer {
  background: var(--color-bg-footer);
  color: var(--color-text-secondary);
  padding: 64px 0 0;
  border-top: 1px solid rgba(212, 175, 55, 0.3);
  position: relative;
  margin-top: 64px;
}

.site-footer::before {
  content: "";
  position: absolute;
  top: -1px;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-bg-primary), var(--color-gold), var(--color-neon-purple));
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr 1fr 1.2fr;
  gap: 40px;
}

.footer-brand .brand-text {
  color: var(--color-gold);
}

.footer-desc {
  margin-top: 12px;
  line-height: 1.7;
  font-size: 0.9rem;
}

.footer-heading {
  font-family: var(--font-title);
  font-size: 1rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-gold);
  margin-bottom: 16px;
  display: inline-block;
}

.footer-heading::after {
  content: "";
  display: block;
  width: 100%;
  height: 1px;
  background: rgba(212, 175, 55, 0.4);
  margin-top: 4px;
}

.site-footer ul {
  list-style: none;
}

.site-footer li {
  margin-bottom: 8px;
}

.site-footer a {
  color: var(--color-text-secondary);
  text-decoration: none;
  transition: color var(--transition-base);
}

.site-footer a:hover {
  color: var(--color-gold);
}

.footer-contact p {
  margin-bottom: 8px;
  line-height: 1.6;
  font-size: 0.9rem;
}

.footer-bottom {
  margin-top: 48px;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
  padding: 20px 0;
  font-size: 0.85rem;
}

.footer-bottom-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 8px;
}

.footer-bottom p {
  margin: 0;
}

/* ===== Breadcrumb ===== */
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  list-style: none;
  padding: 16px 0;
}

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

.breadcrumb li::after {
  content: "/";
  margin-left: 8px;
  opacity: 0.5;
}

.breadcrumb li:last-child::after {
  content: "";
}

.breadcrumb a {
  color: var(--color-text-secondary);
  text-decoration: none;
}

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

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

/* ===== Content Body ===== */
.content-body {
  max-width: 72ch;
  line-height: 1.8;
  color: var(--color-text-primary);
}

.content-body h2,
.content-body h3,
.content-body h4 {
  font-family: var(--font-title);
  margin-top: 2em;
  margin-bottom: 0.5em;
}

.content-body p {
  margin-bottom: 1.5em;
}

.content-body a {
  color: var(--color-gold);
  text-decoration-thickness: 1px;
}

/* ===== Grid ===== */
.grid {
  display: grid;
  gap: 24px;
}

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

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

/* ===== Section ===== */
.section {
  padding: 48px 0;
}

.section-head {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 32px;
}

.section-head h2 {
  font-size: 2rem;
}

.section-head .index-label {
  flex-shrink: 0;
}

/* ===== Index Label ===== */
.index-label {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  letter-spacing: 0.2em;
  color: var(--color-gold);
  text-transform: uppercase;
  border-right: 1px solid var(--color-gold);
  padding-right: 12px;
}

/* ===== Tech Grid Background ===== */
.tech-grid-bg {
  position: relative;
  background-image:
    linear-gradient(rgba(212, 175, 55, 0.08) 1px, transparent 1px),
    linear-gradient(90deg, rgba(212, 175, 55, 0.08) 1px, transparent 1px);
  background-size: 60px 60px;
}

.tech-grid-bg::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: radial-gradient(circle at 20% 20%, rgba(138, 43, 226, 0.12), transparent 50%);
}

/* ===== Image Frame ===== */
.img-frame {
  position: relative;
  overflow: hidden;
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  aspect-ratio: 16 / 9;
}

.img-frame::before {
  content: attr(data-index);
  position: absolute;
  top: 8px;
  left: 8px;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--color-gold);
  z-index: 1;
  background: rgba(11, 27, 58, 0.7);
  padding: 2px 6px;
}

.img-placeholder {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: repeating-linear-gradient(
    45deg,
    rgba(212, 175, 55, 0.03) 0,
    rgba(212, 175, 55, 0.03) 2px,
    transparent 2px,
    transparent 8px
  );
}

.img-placeholder span {
  font-family: var(--font-mono);
  color: var(--color-text-secondary);
  font-size: 0.8rem;
}

.img-frame.is-purple {
  border-color: rgba(138, 43, 226, 0.4);
}

.img-frame.is-purple::before {
  color: var(--color-neon-purple);
}

/* ===== Responsive ===== */
@media (max-width: 1024px) {
  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 768px) {
  body {
    --header-height: 64px;
  }

  .header-inner {
    height: var(--header-height);
  }

  .nav-toggle {
    display: flex;
  }

  .header-cta {
    display: none;
  }

  .nav-cta-mobile {
    display: inline-block;
    margin-top: 8px;
    text-align: center;
  }

  .nav-links {
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    background: rgba(11, 27, 58, 0.98);
    padding: 20px 24px 24px;
    gap: 4px;
    transform: translateY(-8px);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s ease, transform 0.2s ease, visibility 0.2s ease;
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.3);
    max-height: calc(100vh - var(--header-height));
    overflow-y: auto;
  }

  .nav-links[data-open] {
    opacity: 1;
    transform: translateY(0);
    visibility: visible;
  }

  .nav-links a {
    padding: 12px 0;
    border-bottom: 1px solid rgba(212, 175, 55, 0.15);
  }

  .nav-links a::after {
    display: none;
  }

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

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 32px;
  }

  .footer-bottom-inner {
    flex-direction: column;
    text-align: center;
  }
}

@media (min-width: 769px) {
  .nav-links[data-open] {
    pointer-events: auto;
  }
}

/* ===== A11y ===== */
@media (prefers-reduced-motion: reduce) {
  .site-header,
  .nav-links,
  .back-to-top,
  .btn {
    transition: none;
  }
}