/* ==========================================================================
   CoinAd.in — Modern Educational Blockchain UI Framework
   Clean, premium technology publication design system
   ========================================================================== */

:root {
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;

  /* Color Palette - Clean Tech Publication */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --border-color: #e2e8f0;
  --border-subtle: #f1f5f9;

  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --text-subtle: #94a3b8;

  /* Brand Accents (Subtle Blue & Indigo) */
  --accent: #4f46e5;
  --accent-hover: #4338ca;
  --accent-light: #eef2ff;
  --accent-text: #3730a3;

  --success: #10b981;
  --success-bg: #ecfdf5;
  --warning: #f59e0b;
  --warning-bg: #fffbeb;
  --danger: #ef4444;
  --danger-bg: #fef2f2;
  --info: #0284c7;
  --info-bg: #f0f9ff;

  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.07), 0 2px 4px -2px rgb(0 0 0 / 0.05);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.08), 0 4px 6px -4px rgb(0 0 0 / 0.04);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;
  --container-max: 1200px;
}

[data-theme="dark"] {
  --bg-primary: #0b0f17;
  --bg-secondary: #111827;
  --bg-tertiary: #1f2937;
  --bg-card: #141d2e;
  --border-color: #1e293b;
  --border-subtle: #192233;

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-subtle: #64748b;

  --accent: #6366f1;
  --accent-hover: #818cf8;
  --accent-light: #1e1b4b;
  --accent-text: #c7d2fe;

  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.5);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.6);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.7);
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background-color 0.25s ease, color 0.25s ease;
}

main {
  flex: 1;
}

a {
  color: inherit;
  text-decoration: none;
  transition: color 0.15s ease;
}

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

button, input, select, textarea {
  font: inherit;
  color: inherit;
}

/* Container */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: 1.25rem;
  padding-right: 1.25rem;
}

/* Header & Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(8px);
  transition: border-color 0.25s ease;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 4.25rem;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  font-weight: 800;
  font-size: 1.35rem;
  letter-spacing: -0.025em;
  color: var(--text-primary);
}

.brand-icon {
  width: 2rem;
  height: 2rem;
  background: linear-gradient(135deg, #4f46e5, #7c3aed);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #ffffff;
}

.nav-links {
  display: none;
  align-items: center;
  gap: 1.5rem;
}

@media (min-width: 900px) {
  .nav-links {
    display: flex;
  }
}

.nav-link {
  font-size: 0.925rem;
  font-weight: 500;
  color: var(--text-secondary);
  padding: 0.35rem 0.1rem;
  border-bottom: 2px solid transparent;
}

.nav-link:hover, .nav-link.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.btn-icon {
  width: 2.35rem;
  height: 2.35rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.15s ease;
}

.btn-icon:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.mobile-menu-btn {
  display: flex;
}

@media (min-width: 900px) {
  .mobile-menu-btn {
    display: none;
  }
}

/* Mobile Nav Drawer */
.mobile-nav {
  display: none;
  flex-direction: column;
  padding: 1rem 1.25rem 1.5rem;
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
}

.mobile-nav.open {
  display: flex;
}

.mobile-nav a {
  padding: 0.75rem 0;
  font-weight: 500;
  font-size: 1rem;
  border-bottom: 1px solid var(--border-subtle);
}

/* Hero Section */
.hero-section {
  padding: 4.5rem 0 3.5rem;
  background: linear-gradient(180deg, var(--bg-secondary) 0%, var(--bg-primary) 100%);
  border-bottom: 1px solid var(--border-color);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2.5rem;
  align-items: center;
}

@media (min-width: 900px) {
  .hero-grid {
    grid-template-columns: 1.15fr 0.85fr;
  }
}

.badge-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.3rem 0.85rem;
  border-radius: var(--radius-full);
  background: var(--accent-light);
  color: var(--accent-text);
  font-size: 0.825rem;
  font-weight: 600;
  margin-bottom: 1.25rem;
}

.hero-title {
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 1.25rem;
  color: var(--text-primary);
}

@media (min-width: 768px) {
  .hero-title {
    font-size: 3.25rem;
  }
}

.hero-desc {
  font-size: 1.15rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 2rem;
  max-width: 36rem;
}

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

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.75rem 1.4rem;
  font-size: 0.95rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.15s ease;
  text-align: center;
  border: 1px solid transparent;
}

.btn-primary {
  background-color: var(--accent);
  color: #ffffff;
}

.btn-primary:hover {
  background-color: var(--accent-hover);
  box-shadow: 0 4px 12px rgba(79, 70, 229, 0.25);
}

.btn-secondary {
  background-color: var(--bg-card);
  border-color: var(--border-color);
  color: var(--text-primary);
}

.btn-secondary:hover {
  background-color: var(--bg-secondary);
  border-color: var(--text-muted);
}

.hero-illustration {
  display: flex;
  justify-content: center;
}

/* Sections Common */
.section {
  padding: 4rem 0;
}

.section-header {
  margin-bottom: 2.5rem;
}

.section-header.text-center {
  text-align: center;
}

.section-tag {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 700;
  color: var(--accent);
  margin-bottom: 0.4rem;
  display: block;
}

.section-title {
  font-size: 1.85rem;
  font-weight: 800;
  letter-spacing: -0.025em;
  color: var(--text-primary);
}

@media (min-width: 768px) {
  .section-title {
    font-size: 2.25rem;
  }
}

.section-desc {
  font-size: 1.05rem;
  color: var(--text-muted);
  max-width: 38rem;
  margin-top: 0.5rem;
}

.section-header.text-center .section-desc {
  margin-left: auto;
  margin-right: auto;
}

/* Topic Cards */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.topic-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
  display: flex;
  flex-direction: column;
}

.topic-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  border-color: var(--accent);
}

.topic-icon-wrap {
  width: 3rem;
  height: 3rem;
  border-radius: var(--radius-sm);
  background: var(--accent-light);
  color: var(--accent);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1.25rem;
}

.topic-card h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.topic-card p {
  font-size: 0.925rem;
  color: var(--text-secondary);
  line-height: 1.55;
  margin-bottom: 1.25rem;
  flex: 1;
}

.topic-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.85rem;
  color: var(--text-muted);
  font-weight: 500;
  border-top: 1px solid var(--border-subtle);
  padding-top: 1rem;
}

/* Learning Path Timeline */
.path-container {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
}

@media (min-width: 900px) {
  .path-container {
    grid-template-columns: repeat(3, 1fr);
  }
}

.path-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 2rem;
  position: relative;
  box-shadow: var(--shadow-sm);
}

.path-level-badge {
  display: inline-block;
  padding: 0.35rem 0.85rem;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 1rem;
}

.level-1 { background: #dcfce7; color: #15803d; }
.level-2 { background: #e0e7ff; color: #4338ca; }
.level-3 { background: #fef3c7; color: #b45309; }

.path-card h3 {
  font-size: 1.3rem;
  font-weight: 800;
  margin-bottom: 1.25rem;
}

.path-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.path-list-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 0.925rem;
  color: var(--text-secondary);
  transition: color 0.15s ease;
}

.path-list-item:hover {
  color: var(--accent);
}

.path-list-bullet {
  width: 0.5rem;
  height: 0.5rem;
  border-radius: 50%;
  background: var(--accent);
  flex-shrink: 0;
}

/* Article Card Grid */
.article-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 2rem;
}

.article-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.article-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.article-card-media {
  width: 100%;
  aspect-ratio: 16 / 9;
  background: var(--bg-secondary);
  overflow: hidden;
  position: relative;
}

.article-card-media img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.3s ease;
}

.article-card:hover .article-card-media img {
  transform: scale(1.03);
}

.article-card-content {
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  flex: 1;
}

.article-card-meta {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
}

.article-card-category {
  color: var(--accent);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.article-card-title {
  font-size: 1.15rem;
  font-weight: 700;
  line-height: 1.4;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
}

.article-card-title a:hover {
  color: var(--accent);
}

.article-card-excerpt {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.55;
  margin-bottom: 1.25rem;
  flex: 1;
}

.article-card-author {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--border-subtle);
  padding-top: 1rem;
  font-size: 0.825rem;
  color: var(--text-muted);
}

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

.author-avatar-sm {
  width: 1.75rem;
  height: 1.75rem;
  border-radius: 50%;
  background: var(--accent-light);
}

/* Educational Callouts */
.educational-callout {
  padding: 1.25rem 1.5rem;
  border-radius: var(--radius-sm);
  background: var(--info-bg);
  border-left: 4px solid var(--info);
  color: var(--text-primary);
  margin: 1.75rem 0;
  font-size: 0.95rem;
  line-height: 1.6;
}

.educational-callout strong {
  color: var(--info);
}

.educational-callout.alert-warning {
  background: var(--warning-bg);
  border-left-color: var(--warning);
}

.educational-callout.alert-warning strong {
  color: #b45309;
}

/* A-Z Glossary preview */
.letters-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 2rem;
  justify-content: center;
}

.letter-btn {
  width: 2.4rem;
  height: 2.4rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-card);
  font-weight: 700;
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.letter-btn:hover, .letter-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #ffffff;
}

.glossary-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1.25rem;
}

.glossary-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 1.25rem;
  transition: all 0.15s ease;
}

.glossary-card:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-sm);
}

.glossary-card h4 {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 0.35rem;
}

.glossary-card p {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* Article Reader Typography */
.article-reader {
  max-width: 50rem;
  margin: 0 auto;
}

.article-content {
  font-size: 1.1rem;
  line-height: 1.8;
  color: var(--text-primary);
}

.article-content h2 {
  font-size: 1.75rem;
  font-weight: 800;
  margin: 2.25rem 0 1rem;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

.article-content h3 {
  font-size: 1.35rem;
  font-weight: 700;
  margin: 1.75rem 0 0.75rem;
  color: var(--text-primary);
}

.article-content p {
  margin-bottom: 1.4rem;
  color: var(--text-secondary);
}

.article-content ul, .article-content ol {
  margin: 1.25rem 0 1.5rem 1.75rem;
  color: var(--text-secondary);
}

.article-content li {
  margin-bottom: 0.5rem;
}

.article-content code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  padding: 0.15rem 0.35rem;
  border-radius: 4px;
}

.article-content pre {
  background: #0f172a;
  color: #f8fafc;
  padding: 1.25rem;
  border-radius: var(--radius-md);
  overflow-x: auto;
  margin: 1.5rem 0;
  font-size: 0.9rem;
}

.article-content pre code {
  background: transparent;
  border: none;
  color: inherit;
  padding: 0;
}

.article-content blockquote {
  border-left: 4px solid var(--accent);
  padding-left: 1.25rem;
  margin: 1.5rem 0;
  font-style: italic;
  color: var(--text-secondary);
}

/* Table of Contents */
.toc-box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 2.5rem;
}

.toc-title {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.toc-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  font-size: 0.925rem;
}

.toc-list a {
  color: var(--text-secondary);
}

.toc-list a:hover {
  color: var(--accent);
  text-decoration: underline;
}

/* Social Share Bar */
.share-bar {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin: 2rem 0;
  padding: 1rem 0;
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.share-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.45rem 0.85rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-card);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.15s ease;
}

.share-btn:hover {
  background: var(--bg-secondary);
  color: var(--accent);
  border-color: var(--accent);
}

/* Author Box */
.author-box {
  display: flex;
  gap: 1.5rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  margin: 3rem 0;
  align-items: center;
}

.author-box img {
  width: 4.5rem;
  height: 4.5rem;
  border-radius: 50%;
  object-fit: cover;
  flex-shrink: 0;
}

.author-box h4 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
}

.author-box p {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.55;
}

/* Newsletter Box */
.newsletter-box {
  background: linear-gradient(135deg, #1e1b4b 0%, #0f172a 100%);
  color: #ffffff;
  border-radius: var(--radius-lg);
  padding: 3.5rem 2rem;
  text-align: center;
  margin: 4rem 0 2rem;
}

.newsletter-box h2 {
  font-size: 2rem;
  font-weight: 800;
  margin-bottom: 0.75rem;
}

.newsletter-box p {
  font-size: 1.05rem;
  color: #cbd5e1;
  max-width: 34rem;
  margin: 0 auto 2rem;
}

.newsletter-form {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  max-width: 28rem;
  margin: 0 auto;
}

@media (min-width: 640px) {
  .newsletter-form {
    flex-direction: row;
  }
}

.newsletter-input {
  flex: 1;
  padding: 0.85rem 1.25rem;
  border-radius: var(--radius-sm);
  border: 1px solid rgba(255, 255, 255, 0.2);
  background: rgba(255, 255, 255, 0.08);
  color: #ffffff;
  font-size: 0.95rem;
}

.newsletter-input::placeholder {
  color: #94a3b8;
}

.newsletter-input:focus {
  outline: none;
  border-color: #818cf8;
  background: rgba(255, 255, 255, 0.15);
}

/* Footer */
.site-footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: 4.5rem 0 2rem;
  margin-top: auto;
}

.footer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 2.5rem;
  margin-bottom: 3.5rem;
}

.footer-brand {
  grid-column: 1 / -1;
}

@media (min-width: 900px) {
  .footer-brand {
    grid-column: span 1;
  }
}

.footer-brand p {
  font-size: 0.9rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-top: 1rem;
  max-width: 20rem;
}

.footer-col h4 {
  font-size: 0.9rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-primary);
  margin-bottom: 1.25rem;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.footer-links a {
  font-size: 0.9rem;
  color: var(--text-muted);
}

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

.footer-bottom {
  border-top: 1px solid var(--border-color);
  padding-top: 2rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  align-items: center;
  justify-content: space-between;
  font-size: 0.85rem;
  color: var(--text-muted);
}

@media (min-width: 640px) {
  .footer-bottom {
    flex-direction: row;
  }
}

/* Flash Alerts */
.alert {
  padding: 1rem 1.25rem;
  border-radius: var(--radius-sm);
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.95rem;
}

.alert-success { background: var(--success-bg); color: #065f46; border: 1px solid #a7f3d0; }
.alert-error { background: var(--danger-bg); color: #991b1b; border: 1px solid #fecaca; }
.alert-info { background: var(--info-bg); color: #075985; border: 1px solid #bae6fd; }

/* Modal */
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: 100;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 1rem;
}

.modal-backdrop.open {
  display: flex;
}

.modal-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  width: 100%;
  max-width: 34rem;
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

/* Toast */
.toast {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  background: #0f172a;
  color: #ffffff;
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  box-shadow: var(--shadow-lg);
  z-index: 999;
  opacity: 0;
  transform: translateY(10px);
  transition: all 0.25s ease;
  pointer-events: none;
}

.toast.show {
  opacity: 1;
  transform: translateY(0);
}