/* ============================================================
   AI in Education — stylesheet
   ============================================================ */

/* ── Custom properties ─────────────────────────────────────── */
:root {
  /* Brand colors */
  --clr-brand:       #2563eb;
  --clr-brand-dark:  #1d4ed8;
  --clr-brand-light: #dbeafe;
  --clr-accent:      #0ea5e9;

  /* Neutrals */
  --clr-dark:        #0f172a;
  --clr-text:        #1e293b;
  --clr-muted:       #64748b;
  --clr-border:      #e2e8f0;
  --clr-surface:     #f8fafc;
  --clr-white:       #ffffff;

  /* QA section */
  --clr-qa-bg:       #f0f9ff;
  --clr-qa-border:   #bae6fd;

  /* Typography */
  --font-sans:       'Inter', system-ui, -apple-system, sans-serif;
  --font-serif:      'Merriweather', Georgia, serif;

  /* Spacing / layout */
  --max-w:           1100px;
  --max-w-narrow:    760px;
  --radius-sm:       0.375rem;
  --radius:          0.75rem;
  --radius-lg:       1.25rem;

  /* Shadows */
  --shadow-sm:  0 1px 3px rgb(0 0 0 / .08);
  --shadow:     0 4px 14px rgb(0 0 0 / .09);
  --shadow-lg:  0 12px 36px rgb(0 0 0 / .13);

  /* Transitions */
  --ease: 0.22s ease;
}

/* ── Reset ──────────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: var(--font-sans);
  color: var(--clr-text);
  background: var(--clr-white);
  line-height: 1.7;
  font-size: 1rem;
}
img { max-width: 100%; height: auto; display: block; }
a { color: var(--clr-brand); text-decoration: underline; text-underline-offset: 3px; }
a:hover { color: var(--clr-brand-dark); }
button { cursor: pointer; font-family: inherit; }

/* ── Layout containers ──────────────────────────────────────── */
.container {
  width: 100%;
  max-width: var(--max-w);
  margin-inline: auto;
  padding-inline: clamp(1rem, 5vw, 2.5rem);
}
.container--narrow { max-width: var(--max-w-narrow); }

/* ── Buttons ────────────────────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.65rem 1.4rem;
  border-radius: var(--radius);
  font-size: 0.9375rem;
  font-weight: 600;
  text-decoration: none;
  transition: var(--ease);
  border: 2px solid transparent;
  cursor: pointer;
  white-space: nowrap;
}
.btn-primary {
  background: var(--clr-brand);
  color: var(--clr-white);
  border-color: var(--clr-brand);
}
.btn-primary:hover {
  background: var(--clr-brand-dark);
  border-color: var(--clr-brand-dark);
  color: var(--clr-white);
}
.btn-outline {
  background: transparent;
  color: var(--clr-white);
  border-color: rgba(255,255,255,.5);
}
.btn-outline:hover {
  background: rgba(255,255,255,.12);
  border-color: var(--clr-white);
  color: var(--clr-white);
}
.page-footer-nav .btn-outline {
  color: var(--clr-brand);
  border-color: var(--clr-brand);
}
.page-footer-nav .btn-outline:hover {
  background: var(--clr-brand-light);
  color: var(--clr-brand-dark);
}
.btn-sm { padding: 0.45rem 1rem; font-size: 0.875rem; }

/* ── Navigation ─────────────────────────────────────────────── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--clr-dark);
  box-shadow: 0 2px 12px rgb(0 0 0 / .25);
}
.nav-container {
  max-width: var(--max-w);
  margin-inline: auto;
  padding-inline: clamp(1rem, 5vw, 2.5rem);
  display: flex;
  align-items: center;
  gap: 1.5rem;
  height: 64px;
}
.nav-logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
  flex-shrink: 0;
}
.logo-icon {
  font-size: 1.35rem;
  line-height: 1;
}
.logo-text {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--clr-white);
  letter-spacing: -0.01em;
}
.nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  margin-left: auto;
}
.nav-link {
  padding: 0.4rem 0.85rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 500;
  color: rgba(255,255,255,.75);
  text-decoration: none;
  transition: var(--ease);
}
.nav-link:hover,
.nav-link.active {
  color: var(--clr-white);
  background: rgba(255,255,255,.1);
}
.nav-link.active { background: var(--clr-brand); color: var(--clr-white); }
.nav-qa-link {
  background: rgba(14,165,233,.2);
  color: #7dd3fc !important;
}
.nav-qa-link:hover { background: rgba(14,165,233,.35); }

/* Hamburger (mobile) */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  padding: 6px;
  margin-left: auto;
}
.nav-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--clr-white);
  border-radius: 2px;
  transition: var(--ease);
}
.nav-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ── Hero (home page) ───────────────────────────────────────── */
.hero {
  position: relative;
  overflow: hidden;
  background: linear-gradient(135deg, #0f172a 0%, #1e3a5f 50%, #0f172a 100%);
  color: var(--clr-white);
  padding: clamp(4rem, 10vw, 7rem) 0;
  text-align: center;
}
.hero-inner {
  position: relative;
  z-index: 2;
  max-width: 760px;
  margin-inline: auto;
  padding-inline: clamp(1rem, 5vw, 2.5rem);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
}
.hero-badge {
  display: inline-block;
  padding: 0.3rem 1rem;
  background: rgba(37,99,235,.35);
  border: 1px solid rgba(37,99,235,.6);
  border-radius: 50px;
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: #93c5fd;
}
.hero-title {
  font-size: clamp(2rem, 5.5vw, 3.5rem);
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.03em;
}
.hero-subtitle {
  font-size: clamp(1rem, 2vw, 1.2rem);
  color: rgba(255,255,255,.75);
  max-width: 560px;
  line-height: 1.6;
}
.hero-actions { display: flex; gap: 1rem; flex-wrap: wrap; justify-content: center; }

/* Decorative blobs */
.hero-decoration {
  position: absolute;
  inset: 0;
  z-index: 1;
  pointer-events: none;
}
.hero-blob {
  position: absolute;
  border-radius: 50%;
  filter: blur(80px);
  opacity: 0.3;
}
.hero-blob--1 {
  width: 600px; height: 600px;
  background: radial-gradient(circle, #2563eb 0%, transparent 70%);
  top: -200px; left: -150px;
}
.hero-blob--2 {
  width: 500px; height: 500px;
  background: radial-gradient(circle, #0ea5e9 0%, transparent 70%);
  bottom: -150px; right: -100px;
}

/* ── Page hero (subpages) ───────────────────────────────────── */
.page-hero {
  background: linear-gradient(135deg, #0f172a 0%, #1e3a5f 100%);
  color: var(--clr-white);
  padding: 2.5rem 0 3rem;
}
.breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  margin-bottom: 1rem;
}
.breadcrumb-link { color: rgba(255,255,255,.65); text-decoration: none; }
.breadcrumb-link:hover { color: var(--clr-white); }
.breadcrumb-sep { color: rgba(255,255,255,.4); }
.breadcrumb-current { color: var(--clr-white); font-weight: 500; }
.page-hero-title {
  font-size: clamp(1.75rem, 4vw, 2.75rem);
  font-weight: 700;
  letter-spacing: -0.025em;
  line-height: 1.2;
}

/* ── Content / prose ────────────────────────────────────────── */
.content-section { padding: 3.5rem 0; }

.prose {
  font-family: var(--font-serif);
  font-size: 1.0625rem;
  line-height: 1.8;
  color: var(--clr-text);
}
.prose h1, .prose h2, .prose h3, .prose h4 {
  font-family: var(--font-sans);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.02em;
  color: var(--clr-dark);
  margin-top: 2em;
  margin-bottom: 0.6em;
}
.prose h1 { font-size: 2rem; }
.prose h2 { font-size: 1.5rem; padding-bottom: 0.3em; border-bottom: 2px solid var(--clr-border); }
.prose h3 { font-size: 1.2rem; }
.prose h4 { font-size: 1rem; color: var(--clr-muted); text-transform: uppercase; letter-spacing: .06em; }
.prose p { margin-bottom: 1.3em; }
.prose ul, .prose ol { padding-left: 1.5em; margin-bottom: 1.3em; }
.prose li { margin-bottom: 0.4em; }
.prose blockquote {
  border-left: 4px solid var(--clr-brand);
  padding: 0.75rem 1.25rem;
  background: var(--clr-brand-light);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin: 1.5em 0;
  font-style: italic;
  color: var(--clr-muted);
}
.prose blockquote p { margin-bottom: 0.8em; }
.prose blockquote p:last-child { margin-bottom: 0; }
.prose code {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-sm);
  padding: 0.15em 0.4em;
  font-size: 0.875em;
  font-family: 'Fira Code', 'Cascadia Code', Consolas, monospace;
}
.prose pre {
  background: var(--clr-dark);
  color: #e2e8f0;
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin: 1.5em 0;
}
.prose pre code {
  background: none;
  border: none;
  padding: 0;
  font-size: 0.9em;
  color: inherit;
}
.prose table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5em 0;
  font-family: var(--font-sans);
  font-size: 0.9rem;
}
.prose th, .prose td {
  padding: 0.6rem 1rem;
  text-align: left;
  border: 1px solid var(--clr-border);
}
.prose th {
  background: var(--clr-surface);
  font-weight: 600;
}
.prose tr:nth-child(even) td { background: #fafafa; }
.prose a { color: var(--clr-brand); }
.prose hr { border: none; border-top: 2px solid var(--clr-border); margin: 2em 0; }

/* heading anchor links */
.prose .headerlink {
  opacity: 0;
  font-size: 0.75em;
  padding-left: 0.3em;
  text-decoration: none;
  color: var(--clr-muted);
  transition: opacity var(--ease);
}
.prose h2:hover .headerlink,
.prose h3:hover .headerlink { opacity: 1; }

/* ── Topics card grid ───────────────────────────────────────── */
.topics-section {
  background: var(--clr-surface);
  padding: 3.5rem 0;
  border-top: 1px solid var(--clr-border);
  border-bottom: 1px solid var(--clr-border);
}
.section-header {
  text-align: center;
  margin-bottom: 2.5rem;
}
.section-title {
  font-size: clamp(1.5rem, 3vw, 2rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--clr-dark);
}
.section-subtitle {
  margin-top: 0.5rem;
  color: var(--clr-muted);
  font-size: 1rem;
}
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}
.card {
  display: block;
  text-decoration: none;
  background: var(--clr-white);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-lg);
  transition: transform var(--ease), box-shadow var(--ease), border-color var(--ease);
  overflow: hidden;
}
.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--clr-brand);
}
.card-inner {
  padding: 1.75rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  height: 100%;
}
.card-title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--clr-dark);
  letter-spacing: -0.01em;
  line-height: 1.3;
}
.card-description {
  color: var(--clr-muted);
  font-size: 0.9rem;
  line-height: 1.6;
  flex: 1;
}
.card-cta {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  color: var(--clr-brand);
  font-size: 0.875rem;
  font-weight: 600;
  margin-top: 0.5rem;
  transition: gap var(--ease);
}
.card:hover .card-cta { gap: 0.6rem; }

/* ── Q&A accordion ──────────────────────────────────────────── */
.qa-section {
  padding: 3.5rem 0;
  background: var(--clr-qa-bg);
  border-top: 1px solid var(--clr-qa-border);
}
.qa-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  max-width: var(--max-w-narrow);
  margin-inline: auto;
}
.qa-item {
  background: var(--clr-white);
  border: 1px solid var(--clr-qa-border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--ease);
}
.qa-item:hover { box-shadow: var(--shadow); }
.qa-trigger {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.2rem 1.5rem;
  background: none;
  border: none;
  text-align: left;
  font-size: 1rem;
  font-weight: 600;
  color: var(--clr-dark);
  line-height: 1.4;
}
.qa-trigger:focus-visible {
  outline: 3px solid var(--clr-brand);
  outline-offset: -3px;
}
.qa-question-text { flex: 1; }
.qa-icon {
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  background: var(--clr-brand-light);
  border-radius: 50%;
  color: var(--clr-brand);
  transition: transform var(--ease), background var(--ease);
}
.qa-trigger[aria-expanded="true"] .qa-icon {
  transform: rotate(180deg);
  background: var(--clr-brand);
  color: var(--clr-white);
}
.qa-answer {
  padding: 0 1.5rem 1.25rem;
  border-top: 1px solid var(--clr-border);
}
.qa-answer[hidden] { display: none; }
.qa-answer-inner {
  padding-top: 1rem;
  color: var(--clr-text);
  font-size: 0.95rem;
  line-height: 1.75;
}
.qa-answer-inner p {
  margin-top: 0;
  margin-bottom: 1em;
  margin-left: 0;
  margin-right: 0;
}
.qa-answer-inner p:last-child { margin-bottom: 0; }
.qa-answer-inner a { color: var(--clr-brand); }
.qa-answer-inner ul, .qa-answer-inner ol { padding-left: 1.4em; margin-bottom: 0.8em; }
.qa-answer-inner code {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 3px;
  padding: 0.1em 0.35em;
  font-size: 0.875em;
}

/* ── Page footer nav ────────────────────────────────────────── */
.page-footer-nav {
  padding: 2rem 0 3rem;
  border-top: 1px solid var(--clr-border);
}

/* ── Site footer ────────────────────────────────────────────── */
.site-footer {
  background: var(--clr-dark);
  color: rgba(255,255,255,.5);
  padding: 2rem 0;
}
.footer-container {
  max-width: var(--max-w);
  margin-inline: auto;
  padding-inline: clamp(1rem, 5vw, 2.5rem);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 0.5rem;
}
.footer-copy { font-size: 0.875rem; }
.footer-note { font-size: 0.8rem; }

/* ── Responsive ─────────────────────────────────────────────── */
@media (max-width: 768px) {
  .nav-toggle { display: flex; }
  .nav-links {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--clr-dark);
    flex-direction: column;
    align-items: stretch;
    padding: 1rem;
    gap: 0.25rem;
    border-top: 1px solid rgba(255,255,255,.1);
    box-shadow: 0 8px 24px rgb(0 0 0 / .3);
  }
  .nav-links.open { display: flex; }
  .nav-link { padding: 0.75rem 1rem; font-size: 0.95rem; }
  .hero-actions { flex-direction: column; align-items: stretch; text-align: center; }
  .card-grid { grid-template-columns: 1fr; }
  .footer-container { flex-direction: column; text-align: center; }
}

@media (max-width: 480px) {
  .hero { padding: 3rem 0; }
  .content-section { padding: 2rem 0; }
  .topics-section, .qa-section { padding: 2rem 0; }
  .qa-trigger { padding: 1rem 1.1rem; font-size: 0.9375rem; }
}

/* ── Bibliography / Citations ──────────────────────────────── */
.citations {
  margin: 2rem 0;
}

.bibliography {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  margin: 1.5rem 0;
  list-style: none;
  padding: 0;
}

.citation-entry {
  font-weight: 600;
  color: var(--clr-dark);
  margin-bottom: 0.25rem;
  scroll-margin-top: 100px;
}

.citation-entry::before {
  content: "";
  display: block;
  height: 0.5px;
  background: var(--clr-border);
  margin-bottom: 0.5rem;
}

.bibliography dd {
  margin-left: 0;
  color: var(--clr-text);
  line-height: 1.7;
  font-size: 0.95rem;
}

/* When navigating to /citations.html#cite-..., briefly highlight the entry */
.citation-entry:target,
.citation-entry:target + dd {
  border-radius: var(--radius-sm);
}

.citation-entry:target {
  animation: citation-target 2.4s ease-out 1;
}

.citation-entry:target + dd {
  animation: citation-target-detail 2.4s ease-out 1;
}

@keyframes citation-target {
  0% {
    background: var(--clr-brand-light);
    box-shadow: 0 0 0 6px var(--clr-brand-light);
  }
  60% {
    background: var(--clr-brand-light);
    box-shadow: 0 0 0 6px var(--clr-brand-light);
  }
  100% {
    background: transparent;
    box-shadow: 0 0 0 0 var(--clr-brand-light);
  }
}

@keyframes citation-target-detail {
  0% {
    box-shadow: 0 0 0 6px var(--clr-brand-light);
  }
  60% {
    box-shadow: 0 0 0 6px var(--clr-brand-light);
  }
  100% {
    box-shadow: 0 0 0 0 var(--clr-brand-light);
  }
}

/* ── Utility / scroll ───────────────────────────────────────── */
:focus-visible { outline: 3px solid var(--clr-brand); outline-offset: 3px; }

/* Smooth accordion animation (added by JS) */
.qa-answer.animating { display: block !important; overflow: hidden; }