/* =========================================================
   High Performance Spark — Landing Page Styles
   ========================================================= */

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

:root {
  --color-bg:        #0a0c10;
  --color-surface:   #111318;
  --color-surface2:  #181c24;
  --color-border:    #252a35;
  --color-text:      #e8ecf0;
  --color-muted:     #8b92a0;
  --color-spark:     #f5720a;    /* Spark orange */
  --color-spark-lt:  #ff9340;
  --color-accent:    #3b82f6;
  --color-code:      #a8d4ff;
  --font-sans:       'Inter', system-ui, sans-serif;
  --font-mono:       'JetBrains Mono', 'Fira Code', monospace;
  --radius:          12px;
  --shadow-card:     0 4px 24px rgba(0,0,0,0.45);
  --transition:      220ms ease;
}

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--color-spark-lt); text-decoration: none; }
a:hover { text-decoration: underline; }
img { max-width: 100%; display: block; }

/* --- Layout --------------------------------------------- */
.container {
  max-width: 1120px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

section { padding: 5rem 0; }

/* --- Navigation ----------------------------------------- */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(10,12,16,0.9);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
}

.site-nav .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 1rem;
  padding-bottom: 1rem;
}

.nav-brand {
  font-weight: 700;
  font-size: 1rem;
  color: var(--color-text);
  letter-spacing: -0.02em;
}
.nav-brand span { color: var(--color-spark); }

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--color-muted);
  font-size: 0.9rem;
  font-weight: 500;
  transition: color var(--transition);
}
.nav-links a:hover { color: var(--color-text); text-decoration: none; }

.nav-cta .btn-primary { font-size: 0.875rem; padding: 0.55rem 1.25rem; }

/* --- Hero ----------------------------------------------- */
.hero {
  padding: 6rem 0 5rem;
  background: radial-gradient(ellipse 80% 50% at 50% -10%, rgba(245,114,10,0.18) 0%, transparent 60%);
}

.hero-inner {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 4rem;
  align-items: center;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(245,114,10,0.12);
  border: 1px solid rgba(245,114,10,0.3);
  color: var(--color-spark-lt);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: 0.35rem 0.85rem;
  border-radius: 100px;
  margin-bottom: 1.25rem;
}

.hero h1 {
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 800;
  letter-spacing: -0.04em;
  line-height: 1.1;
  margin-bottom: 0.5rem;
}

.hero h1 span { color: var(--color-spark); }

.hero-subtitle {
  font-size: 1.15rem;
  color: var(--color-muted);
  margin-bottom: 0.5rem;
}

.hero-edition {
  font-size: 0.85rem;
  color: var(--color-spark-lt);
  font-weight: 600;
  margin-bottom: 1.5rem;
  letter-spacing: 0.03em;
}

.hero-authors {
  font-size: 1rem;
  color: var(--color-muted);
  margin-bottom: 2.25rem;
}

.hero-authors strong { color: var(--color-text); }

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

/* Book Cover */
.book-cover-wrap {
  flex-shrink: 0;
  /* Reserve space so the layout never collapses while cover art is pending */
  min-width: 220px;
  width: 220px;
}

.book-cover {
  width: 220px;
  height: auto;
  border-radius: 8px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.7), 0 0 0 1px rgba(255,255,255,0.06);
  transform: perspective(800px) rotateY(-6deg);
  transition: transform 0.4s ease;
  display: block;
}

.book-cover:hover {
  transform: perspective(800px) rotateY(0deg);
}

/* Book cover placeholder SVG */
.book-cover-placeholder {
  width: 220px;
  height: 308px;
  border-radius: 8px;
  background: linear-gradient(145deg, #1a1f2e 0%, #0f1117 100%);
  border: 1px solid var(--color-border);
  box-shadow: 0 20px 60px rgba(0,0,0,0.7), 0 0 0 1px rgba(255,255,255,0.06);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  text-align: center;
  transform: perspective(800px) rotateY(-6deg);
  transition: transform 0.4s ease;
}

.book-cover-placeholder:hover {
  transform: perspective(800px) rotateY(0deg);
}

.book-cover-placeholder .cover-publisher {
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-muted);
  margin-bottom: 1rem;
}

.book-cover-placeholder .cover-spark-icon {
  font-size: 3rem;
  margin-bottom: 1rem;
}

.book-cover-placeholder .cover-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--color-text);
  line-height: 1.3;
  margin-bottom: 0.5rem;
}

.book-cover-placeholder .cover-subtitle {
  font-size: 0.6rem;
  color: var(--color-muted);
  line-height: 1.4;
  margin-bottom: 1rem;
}

.book-cover-placeholder .cover-edition {
  font-size: 0.6rem;
  font-weight: 600;
  color: var(--color-spark-lt);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  background: rgba(245,114,10,0.12);
  border: 1px solid rgba(245,114,10,0.25);
  border-radius: 4px;
  padding: 0.2rem 0.5rem;
  margin-bottom: 1rem;
}

.book-cover-placeholder .cover-authors {
  font-size: 0.6rem;
  color: var(--color-muted);
  font-style: italic;
}

/* --- Buttons -------------------------------------------- */
.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: linear-gradient(135deg, var(--color-spark) 0%, #e05800 100%);
  color: #fff;
  font-weight: 700;
  font-size: 1rem;
  padding: 0.8rem 1.75rem;
  border-radius: 8px;
  transition: all var(--transition);
  box-shadow: 0 4px 14px rgba(245,114,10,0.35);
  white-space: nowrap;
}

.btn-primary:hover {
  background: linear-gradient(135deg, var(--color-spark-lt) 0%, var(--color-spark) 100%);
  box-shadow: 0 6px 20px rgba(245,114,10,0.5);
  transform: translateY(-1px);
  text-decoration: none;
  color: #fff;
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: transparent;
  color: var(--color-text);
  font-weight: 600;
  font-size: 1rem;
  padding: 0.8rem 1.75rem;
  border-radius: 8px;
  border: 1px solid var(--color-border);
  transition: all var(--transition);
  white-space: nowrap;
}

.btn-secondary:hover {
  background: var(--color-surface);
  border-color: var(--color-muted);
  text-decoration: none;
  color: var(--color-text);
  transform: translateY(-1px);
}

/* --- Stats Bar ------------------------------------------ */
.stats-bar {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
  padding: 2rem 0;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 2rem;
  text-align: center;
}

.stat-value {
  font-size: 2rem;
  font-weight: 800;
  color: var(--color-spark-lt);
  letter-spacing: -0.03em;
}

.stat-label {
  font-size: 0.8rem;
  color: var(--color-muted);
  font-weight: 500;
  margin-top: 0.25rem;
}

/* --- About Section -------------------------------------- */
.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 3rem;
  align-items: start;
}

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

.section-title {
  font-size: clamp(1.75rem, 3vw, 2.5rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  margin-bottom: 1.25rem;
}

.section-desc {
  font-size: 1.05rem;
  color: var(--color-muted);
  line-height: 1.75;
  margin-bottom: 1.25rem;
}

.chapter-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
}

.chapter-list li {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  font-size: 0.95rem;
  color: var(--color-muted);
}

.chapter-list li::before {
  content: "▸";
  color: var(--color-spark);
  font-size: 0.75rem;
  margin-top: 0.25rem;
  flex-shrink: 0;
}

/* --- Topics Grid ---------------------------------------- */
.topics-section { background: var(--color-surface); }

.topics-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
  margin-top: 3rem;
}

.topic-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.75rem;
  transition: all var(--transition);
}

.topic-card:hover {
  border-color: rgba(245,114,10,0.4);
  box-shadow: 0 0 0 1px rgba(245,114,10,0.15), var(--shadow-card);
  transform: translateY(-2px);
}

.topic-icon {
  font-size: 2rem;
  margin-bottom: 1rem;
}

.topic-title {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 0.6rem;
}

.topic-desc {
  font-size: 0.875rem;
  color: var(--color-muted);
  line-height: 1.6;
}

/* --- Authors Section ------------------------------------ */
.authors-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 2rem;
  margin-top: 3rem;
}

.author-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 2rem;
  display: flex;
  gap: 1.25rem;
  transition: border-color var(--transition);
}

.author-card:hover { border-color: rgba(245,114,10,0.35); }

.author-avatar {
  width: 72px;
  height: 72px;
  border-radius: 50%;
  border: 2px solid var(--color-spark);
  overflow: hidden;
  flex-shrink: 0;
  background: var(--color-surface2);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.75rem;
}

.author-info h3 {
  font-size: 1.1rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.author-info p {
  font-size: 0.875rem;
  color: var(--color-muted);
  line-height: 1.6;
  margin-bottom: 0.75rem;
}

.author-links {
  display: flex;
  gap: 0.75rem;
}

.author-link {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-accent);
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}

.author-link:hover { text-decoration: underline; }

/* --- Example Repos Section ------------------------------ */
.repos-section { background: var(--color-surface); }

.repos-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin-top: 3rem;
}

.repo-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.75rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  transition: all var(--transition);
  text-decoration: none;
  color: var(--color-text);
}

.repo-card:hover {
  border-color: rgba(59,130,246,0.5);
  box-shadow: 0 0 0 1px rgba(59,130,246,0.15), var(--shadow-card);
  transform: translateY(-2px);
  text-decoration: none;
  color: var(--color-text);
}

.repo-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
}

.repo-name {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--color-accent);
}

.repo-stars {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  font-size: 0.8rem;
  color: var(--color-muted);
  white-space: nowrap;
}

.repo-desc {
  font-size: 0.9rem;
  color: var(--color-muted);
  line-height: 1.65;
  flex: 1;
}

.repo-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.repo-lang {
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--color-muted);
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.repo-lang::before {
  content: "";
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--color-spark);
  display: inline-block;
}

.repo-github-link {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-accent);
  margin-left: auto;
}

/* --- CTA Section ---------------------------------------- */
.cta-section {
  background: radial-gradient(ellipse 80% 80% at 50% 50%, rgba(245,114,10,0.12) 0%, transparent 70%);
  text-align: center;
}

.cta-section .section-title { margin-bottom: 1rem; }
.cta-section .section-desc { max-width: 560px; margin: 0 auto 2.5rem; }

.cta-buttons {
  display: flex;
  gap: 1rem;
  justify-content: center;
  flex-wrap: wrap;
}

.purchase-grid {
  display: flex;
  gap: 1rem;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 1.25rem;
}

.purchase-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-muted);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 0.6rem 1.25rem;
  transition: all var(--transition);
}

.purchase-link:hover {
  color: var(--color-text);
  border-color: var(--color-muted);
  background: var(--color-surface2);
  text-decoration: none;
}

/* --- Cross-reference Strip ------------------------------- */
.crossref-strip {
  background: var(--color-surface2);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
  padding: 1.5rem 0;
}

.crossref-inner {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  flex-wrap: wrap;
  justify-content: center;
  text-align: center;
}

.crossref-intro {
  font-size: 0.9rem;
  color: var(--color-muted);
  font-style: italic;
  white-space: nowrap;
}

.crossref-links {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
  justify-content: center;
}

.crossref-link {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 0.6rem 1rem;
  text-decoration: none;
  color: var(--color-text);
  transition: all var(--transition);
}

.crossref-link:hover {
  border-color: var(--color-spark-lt);
  background: var(--color-bg);
  text-decoration: none;
  color: var(--color-text);
  transform: translateY(-1px);
}

.crossref-emoji {
  font-size: 1.4rem;
  line-height: 1;
}

.crossref-text {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 0.1rem;
  text-align: left;
}

.crossref-text strong {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--color-text);
}

.crossref-text span {
  font-size: 0.75rem;
  color: var(--color-spark-lt);
  font-family: var(--font-mono);
}

.crossref-divider {
  color: var(--color-border);
  font-size: 1.25rem;
  user-select: none;
}

/* --- Footer --------------------------------------------- */
.site-footer {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: 2rem 0;
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-copy {
  font-size: 0.875rem;
  color: var(--color-muted);
}

.footer-nav {
  display: flex;
  gap: 1.5rem;
}

.footer-nav a {
  font-size: 0.875rem;
  color: var(--color-muted);
  transition: color var(--transition);
}

.footer-nav a:hover { color: var(--color-text); text-decoration: none; }

/* --- Divider -------------------------------------------- */
.section-divider {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 0;
}

/* --- Responsive ----------------------------------------- */
@media (max-width: 900px) {
  .hero-inner { grid-template-columns: 1fr; }
  .book-cover-wrap { order: -1; margin: 0 auto; }
  .about-grid { grid-template-columns: 1fr; }
  .topics-grid { grid-template-columns: repeat(2, 1fr); }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .crossref-inner { flex-direction: column; gap: 1rem; }
  .crossref-intro { white-space: normal; }
}

@media (max-width: 640px) {
  section { padding: 3.5rem 0; }
  .hero { padding: 4rem 0 3rem; }
  .hero h1 { font-size: 2.25rem; }
  .topics-grid { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .nav-links { display: none; }
  .hero-actions { flex-direction: column; }
  .hero-actions .btn-primary,
  .hero-actions .btn-secondary { width: 100%; justify-content: center; }
  .crossref-links { flex-direction: column; align-items: stretch; }
  .crossref-divider { display: none; }
}