/* ===================================================
   learn-with-ai — Landing Page CSS  (Light theme)
   =================================================== */

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

:root {
  --bg:              #f8fafc;
  --bg-card:         #ffffff;
  --bg-code:         #f1f5f9;
  --border:          #e2e8f0;
  --border-dark:     #cbd5e1;
  --text:            #0f172a;
  --text-muted:      #64748b;
  --text-light:      #94a3b8;
  --accent:          #2563eb;
  --accent-light:    #eff6ff;
  --accent-sub:      #16a34a;
  --accent-sub-light:#f0fdf4;
  --warn:            #d97706;
  --warn-light:      #fffbeb;
  --accent-doc:      #7c3aed;
  --accent-doc-light:#f5f3ff;
  --radius:          10px;
  --radius-lg:       16px;
  --max-w:           1100px;
  --sidebar-w:       270px;
  --shadow-sm:       0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.05);
  --shadow-md:       0 4px 12px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);
}

html { scroll-behavior: smooth; scroll-padding-top: 60px; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
}

/* ============================================================
   Layout — sidebar + main
   ============================================================ */
.page-wrapper {
  display: flex;
  min-height: 100vh;
  padding-top: 60px;
}
.sidebar {
  position: fixed;
  top: 60px; left: 0;
  width: var(--sidebar-w);
  height: calc(100vh - 60px);
  overflow-y: auto;
  background: var(--bg-card);
  border-right: 1px solid var(--border);
  padding: 16px 0;
  z-index: 90;
}
.sidebar-heading {
  font-size: 10px; font-weight: 700; letter-spacing: .1em;
  text-transform: uppercase; color: var(--text-light);
  padding: 0 18px; margin: 16px 0 6px;
}
.sidebar a {
  display: flex; align-items: center; gap: 8px;
  padding: 7px 18px;
  font-size: 13px; color: var(--text-muted); text-decoration: none;
  border-left: 2px solid transparent;
  transition: background .15s, color .15s, border-color .15s;
  line-height: 1.3;
}
.sidebar a:hover { background: var(--bg); color: var(--text); }
.sidebar a.active {
  color: var(--accent); border-left-color: var(--accent);
  background: var(--accent-light); font-weight: 600;
}
.badge-sb {
  font-size: 10px; font-weight: 700; padding: 2px 7px;
  border-radius: 8px; flex-shrink: 0;
}
.sb-text { font-size: 11px; line-height: 1.3; flex: 1; }
.badge-sb-b { background: var(--accent-sub-light); color: var(--accent-sub); }
.badge-sb-m { background: var(--accent-light); color: var(--accent); }
.badge-sb-a { background: var(--warn-light); color: var(--warn); }
.badge-sb-d { background: var(--accent-doc-light); color: var(--accent-doc); }

.main-content { flex: 1; margin-left: var(--sidebar-w); min-width: 0; }
.container { max-width: 960px; margin: 0 auto; padding: 0 32px; }
section { padding: 72px 0; border-bottom: 1px solid var(--border); position: relative; }
section:last-of-type { border-bottom: none; }

/* ============================================================
   Section backgrounds & decoration
   ============================================================ */
/* Tinted sections — light blue wash + radial glow */
#why, #about, #faq,
#problem, #scoring,
#essential, #ui {
  background-color: #f0f6ff;
  background-image: radial-gradient(circle at 92% 88%, rgba(37,99,235,.11) 0%, transparent 52%);
}
/* Grid sections — subtle dot grid */
#curriculum, #siteflow, #structure {
  background-color: var(--bg-card);
  background-image:
    linear-gradient(rgba(37,99,235,.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(37,99,235,.05) 1px, transparent 1px);
  background-size: 40px 40px;
}

/* ============================================================
   Header
   ============================================================ */
header {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  height: 60px; background: rgba(255,255,255,.94);
  backdrop-filter: blur(8px); border-bottom: 1px solid var(--border);
  display: flex; align-items: center;
}
header .hdr-inner {
  display: flex; align-items: center; justify-content: space-between; gap: 16px;
  width: 100%; padding: 0 24px 0 calc(var(--sidebar-w) + 24px);
}
.logo { font-weight: 800; font-size: 15px; color: var(--text); text-decoration: none; letter-spacing: -.01em; }
.logo span { color: var(--accent); }
nav { display: flex; gap: 20px; align-items: center; }
nav a { color: var(--text-muted); text-decoration: none; font-size: 13.5px; font-weight: 500; transition: color .2s; }
nav a:hover { color: var(--text); }
.nav-toggle {
  display: none; flex-direction: column; justify-content: center; gap: 5px;
  background: none; border: none; cursor: pointer; padding: 4px; flex-shrink: 0;
}
.nav-toggle span {
  display: block; width: 22px; height: 2px;
  background: var(--text); border-radius: 2px;
  transition: transform .25s, opacity .25s;
}
.nav-toggle.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle.open span:nth-child(2) { opacity: 0; }
.nav-toggle.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ============================================================
   Hero
   ============================================================ */
#hero {
  padding: 0; border-bottom: 1px solid var(--border);
  background: #0a0f1e url(hero.png) center / cover no-repeat;
  overflow: hidden; position: relative;
}
#hero::before {
  content: ''; position: absolute; inset: 0;
  background: linear-gradient(100deg, rgba(10,15,30,.88) 0%, rgba(10,15,30,.65) 52%, rgba(10,15,30,.22) 100%);
  pointer-events: none;
}
.hero-inner {
  max-width: 680px;
  padding: 96px 32px 88px;
  position: relative;
  z-index: 1;
}

/* Hero text on dark cover */
#hero .hero-badge {
  color: rgba(255,255,255,.88);
  background: rgba(255,255,255,.13);
  border-color: rgba(255,255,255,.22);
}
#hero h1 { color: #fff; }
#hero h1 em { color: #93c5fd; }
#hero .hero-sub { color: rgba(255,255,255,.72); }
#hero .btn-secondary {
  background: rgba(255,255,255,.1); color: #fff;
  border-color: rgba(255,255,255,.32);
}
#hero .btn-secondary:hover {
  background: rgba(255,255,255,.2); border-color: rgba(255,255,255,.6);
}

.hero-badge {
  display: inline-flex; align-items: center; gap: 6px;
  font-size: 11px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase;
  color: var(--accent-sub); background: var(--accent-sub-light);
  border: 1px solid rgba(22,163,74,.2);
  padding: 4px 12px; border-radius: 20px; margin-bottom: 20px;
}
h1 {
  font-size: clamp(24px, 3.5vw, 40px); font-weight: 800; line-height: 1.2;
  letter-spacing: -.025em; margin-bottom: 18px; color: var(--text);
}
h1 em { font-style: normal; color: var(--accent); }
.hero-sub {
  font-size: 15px; color: var(--text-muted);
  max-width: 680px; margin-bottom: 36px; line-height: 1.75;
}
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; }

/* ============================================================
   Buttons
   ============================================================ */
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 10px 22px; border-radius: var(--radius);
  font-size: 14px; font-weight: 600; text-decoration: none;
  transition: all .18s; box-shadow: var(--shadow-sm);
}
.btn:hover { transform: translateY(-1px); box-shadow: var(--shadow-md); }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: #1d4ed8; }
.btn-secondary { background: var(--bg-card); color: var(--text); border: 1px solid var(--border-dark); }
.btn-secondary:hover { border-color: var(--accent); color: var(--accent); }
.btn-ghost { background: transparent; color: var(--accent); border: 1px solid var(--accent); box-shadow: none; }
.btn-ghost:hover { background: var(--accent-light); }

/* ============================================================
   Headings
   ============================================================ */
h2 { font-size: clamp(18px, 2.5vw, 24px); font-weight: 700; margin-bottom: 10px; letter-spacing: -.01em; color: #1e293b; }
section:not(.cta-strip) .container > h2 {
  display: flex; align-items: center; gap: 10px;
}
section:not(.cta-strip) .container > h2::before {
  content: '';
  flex-shrink: 0; display: block;
  width: 4px; height: 1.1em;
  background: linear-gradient(180deg, var(--accent) 0%, var(--accent-sub) 100%);
  border-radius: 2px;
}
.section-lead { color: var(--text-muted); margin-bottom: 36px; max-width: 750px; font-size: 15px; }

/* ============================================================
   Cards
   ============================================================ */
.cards { display: grid; gap: 16px; }
.cards-3 { grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); }
.cards-2 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 24px; box-shadow: var(--shadow-sm);
  transition: box-shadow .2s, transform .2s;
  position: relative; overflow: hidden;
}
.card::after {
  content: '';
  position: absolute; bottom: -18px; right: -18px;
  width: 100px; height: 100px;
  background: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' width='100' height='100' viewBox='0 0 100 100'><circle cx='84' cy='84' r='60' fill='none' stroke='%232563eb' stroke-width='1.5'/><circle cx='84' cy='84' r='40' fill='none' stroke='%232563eb' stroke-width='1.5'/><circle cx='84' cy='84' r='20' fill='none' stroke='%232563eb' stroke-width='1.5'/></svg>") center / contain no-repeat;
  opacity: .06;
  pointer-events: none;
  transition: opacity .2s;
}
.card:hover::after { opacity: .1; }
.card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); }
.card-num { font-size: 26px; font-weight: 800; color: var(--accent); line-height: 1; margin-bottom: 10px; }
.card h3 { font-size: 15px; font-weight: 700; margin-bottom: 8px; }
.card p { font-size: 13.5px; color: var(--text-muted); line-height: 1.6; }

/* ============================================================
   Curriculum / Questions index
   ============================================================ */
.q-section-heading {
  display: block;
  margin: 64px 0 24px;
  padding: 24px 28px 20px 32px;
  border-radius: var(--radius-lg);
  border: 1px solid transparent;
  border-left-width: 4px;
  box-shadow: 0 4px 20px rgba(0,0,0,.07), 0 1px 4px rgba(0,0,0,.04);
  position: relative; overflow: hidden;
}
.q-section-heading:has(.badge-b) {
  background: linear-gradient(135deg, rgba(22,163,74,.09) 0%, rgba(22,163,74,.02) 65%);
  border-color: rgba(22,163,74,.2);
  border-left-color: var(--accent-sub);
}
.q-section-heading:has(.badge-m) {
  background: linear-gradient(135deg, rgba(37,99,235,.08) 0%, rgba(37,99,235,.02) 65%);
  border-color: rgba(37,99,235,.18);
  border-left-color: var(--accent);
}
.q-section-heading:has(.badge-a) {
  background: linear-gradient(135deg, rgba(217,119,6,.09) 0%, rgba(217,119,6,.02) 65%);
  border-color: rgba(217,119,6,.2);
  border-left-color: var(--warn);
}
.q-section-heading .badge {
  display: block;
  font-size: 42px; font-weight: 900; line-height: 1; letter-spacing: -.035em;
  padding: 0; border-radius: 0; background: transparent !important;
  margin-bottom: 8px;
}
.q-section-heading:has(.badge-b) .badge { color: var(--accent-sub); }
.q-section-heading:has(.badge-m) .badge { color: var(--accent); }
.q-section-heading:has(.badge-a) .badge { color: var(--warn); }
.q-section-heading h3 { font-size: 14px; font-weight: 600; color: var(--text-muted); margin: 0; }
.q-section-line { display: none; }
.curriculum { display: grid; gap: 10px; }
.q-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 20px 24px; box-shadow: var(--shadow-sm);
  display: grid; grid-template-columns: 46px 1fr; gap: 0 16px;
  transition: box-shadow .2s;
}
.q-card:hover { box-shadow: var(--shadow-md); }
.q-num { font-size: 13px; font-weight: 800; color: var(--text-light); padding-top: 2px; }
.q-body h4 { font-size: 16px; font-weight: 800; margin-bottom: 6px; line-height: 1.3; }
.q-body .q-scenario { font-size: 14px; color: var(--text-muted); margin-bottom: 10px; line-height: 1.6; }
.q-points { list-style: none; display: flex; flex-wrap: wrap; gap: 5px; }
.q-points li {
  font-size: 11.5px; background: var(--bg); border: 1px solid var(--border);
  padding: 2px 9px; border-radius: 20px; color: var(--text-muted);
}

/* ============================================================
   Difficulty table
   ============================================================ */
.diff-table { width: 100%; border-collapse: collapse; font-size: 14px; }
.diff-table th, .diff-table td { text-align: left; padding: 12px 14px; border-bottom: 1px solid var(--border); }
.diff-table th { color: var(--text-muted); font-weight: 600; font-size: 11px; text-transform: uppercase; letter-spacing: .06em; background: var(--bg); }
.diff-table tr:last-child td { border-bottom: none; }
.diff-table tbody tr:hover td { background: var(--bg); }
.badge { display: inline-block; padding: 2px 10px; border-radius: 12px; font-size: 12px; font-weight: 600; }
.badge-b { background: var(--accent-sub-light); color: var(--accent-sub); }
.badge-m { background: var(--accent-light); color: var(--accent); }
.badge-a { background: var(--warn-light); color: var(--warn); }
.badge-d { background: var(--accent-doc-light); color: var(--accent-doc); }

/* ============================================================
   Documentation accent & series tabs
   ============================================================ */
.q-section-heading:has(.badge-d) {
  background: linear-gradient(135deg, rgba(124,58,237,.08) 0%, rgba(124,58,237,.02) 65%);
  border-color: rgba(124,58,237,.18);
  border-left-color: var(--accent-doc);
}
.q-section-heading:has(.badge-d) .badge { color: var(--accent-doc); }
.series-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 32px;
  background: var(--bg-code);
  border-radius: 12px;
  padding: 4px;
}
.series-tab {
  flex: 1;
  padding: 9px 4px;
  font-size: 13px; font-weight: 600;
  border: none;
  background: transparent; color: var(--text-muted);
  cursor: pointer;
  display: flex; flex-direction: column; align-items: center; gap: 2px;
  transition: color .18s, background .18s, box-shadow .18s;
  border-radius: 9px;
  text-align: center; line-height: 1.3;
}
.seg-label { font-size: 11px; font-weight: 700; pointer-events: none; }
.seg-count { font-size: 14px; font-weight: 400; opacity: .8; pointer-events: none; }
.series-tab:hover { color: var(--text); background: rgba(255,255,255,.65); }
.series-tab.active { color: var(--accent); background: #fff; box-shadow: 0 1px 4px rgba(0,0,0,.13); }
.series-panel[hidden] { display: none; }

/* ============================================================
   Code block
   ============================================================ */
.code-block {
  background: var(--bg-code); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px 24px;
  font-family: "SFMono-Regular", "Cascadia Mono", Consolas, monospace;
  font-size: 12.5px; line-height: 1.8; overflow-x: auto; white-space: pre; color: #334155;
}
.code-block .dir { color: var(--accent); font-weight: 700; }
.code-block .note { color: var(--text-light); }

/* ============================================================
   Callout
   ============================================================ */
.callout {
  background: var(--accent-light); border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0; padding: 16px 20px;
  font-size: 15px; color: #1e40af; line-height: 1.7; margin-top: 28px;
}

/* ============================================================
   FAQ
   ============================================================ */
.faq-list { display: grid; gap: 10px; }
.faq-item { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius-lg); padding: 18px 22px; box-shadow: var(--shadow-sm); }
.faq-q { font-weight: 700; margin-bottom: 8px; font-size: 14.5px; }
.faq-a { font-size: 13.5px; color: var(--text-muted); }

/* ============================================================
   Related materials list
   ============================================================ */
.related-list {
  display: flex;
  flex-direction: column;
  gap: 20px;
}
.related-item {
  position: relative;
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 24px;
  align-items: start;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px;
  text-decoration: none;
  color: inherit;
  transition: box-shadow .18s, border-color .18s;
}
.related-item:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 16px rgba(37,99,235,.08);
}
.related-item-thumb {
  width: 100%;
  aspect-ratio: 1200 / 630;
  object-fit: cover;
  border-radius: 8px;
  background: var(--bg-code);
  display: block;
}
.related-item-body { display: flex; flex-direction: column; gap: 8px; }
.related-item-tag { font-size: 11.5px; font-weight: 700; color: var(--text-muted); letter-spacing: .04em; text-transform: uppercase; }
.related-item-title { font-size: 16px; font-weight: 700; color: var(--text); line-height: 1.4; }
.related-item-desc { font-size: 13.5px; color: var(--text-muted); line-height: 1.75; margin: 0; }
.related-item-ext {
  position: absolute; top: 14px; right: 16px;
  color: var(--text-muted); opacity: .45;
  transition: opacity .18s, color .18s;
  line-height: 1;
}
.related-item:hover .related-item-ext { opacity: 1; color: var(--accent); }
@media (max-width: 600px) {
  .related-item { grid-template-columns: 1fr; gap: 14px; }
}

/* ============================================================
   CTA strip
   ============================================================ */
.cta-strip {
  text-align: center; padding: 80px 0;
  background: linear-gradient(135deg, #eff6ff 0%, #f8fafc 100%);
  border-bottom: none !important;
}
.cta-strip h2 { margin-bottom: 12px; }
.cta-strip p { color: var(--text-muted); margin-bottom: 32px; font-size: 15px; }
.cta-strip .hero-cta { justify-content: center; }

/* ============================================================
   Footer
   ============================================================ */
footer {
  padding: 28px 0; border-top: 1px solid var(--border);
  font-size: 13px; color: var(--text-muted); text-align: center; background: var(--bg-card);
}
footer a { color: var(--text-muted); text-decoration: underline; }
footer a:hover { color: var(--text); }

/* ============================================================
   Hero entry animation
   ============================================================ */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(24px); }
  to   { opacity: 1; transform: translateY(0); }
}
#hero .hero-badge { animation: fadeUp .5s .05s both cubic-bezier(.22,.61,.36,1); }
#hero h1          { animation: fadeUp .65s .2s  both cubic-bezier(.22,.61,.36,1); }
#hero .hero-sub   { animation: fadeUp .65s .35s both cubic-bezier(.22,.61,.36,1); }
#hero .hero-cta   { animation: fadeUp .65s .5s  both cubic-bezier(.22,.61,.36,1); }

/* ============================================================
   Scroll reveal
   ============================================================ */
.reveal, .reveal-left, .reveal-scale { will-change: opacity, transform; }
.reveal {
  opacity: 0; transform: translateY(32px);
  transition: opacity .65s cubic-bezier(.22,.61,.36,1), transform .65s cubic-bezier(.22,.61,.36,1);
}
.reveal-left {
  opacity: 0; transform: translateX(-36px);
  transition: opacity .65s cubic-bezier(.22,.61,.36,1), transform .65s cubic-bezier(.22,.61,.36,1);
}
.reveal-scale {
  opacity: 0; transform: scale(.96);
  transition: opacity .6s cubic-bezier(.22,.61,.36,1), transform .6s cubic-bezier(.22,.61,.36,1);
}
.reveal.is-visible, .reveal-left.is-visible, .reveal-scale.is-visible {
  opacity: 1; transform: none;
}

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 900px) {
  .sidebar { display: none; }
  .main-content { margin-left: 0; }
  header .hdr-inner { padding: 0 20px; }
  .hero-inner { padding: 64px 24px 56px; }
}
@media (max-width: 720px) {
  .hero-inner { padding: 52px 20px 44px; max-width: 100%; }
  .q-section-heading .badge { font-size: 32px; }
}
@media (max-width: 600px) {
  .nav-toggle { display: flex; }
  nav {
    display: none; position: absolute; top: 60px; left: 0; right: 0;
    background: rgba(255,255,255,.97); backdrop-filter: blur(8px);
    border-bottom: 1px solid var(--border);
    flex-direction: column; gap: 0; padding: 8px 20px 12px;
  }
  nav.open { display: flex; }
  nav a { padding: 11px 4px; border-bottom: 1px solid var(--border); font-size: 14px; width: 100%; }
  nav a:last-child { border-bottom: none; }
  .hero-cta { flex-direction: column; }
  .btn { justify-content: center; }
  section { padding: 48px 0; }
  .q-card { grid-template-columns: 1fr; }
  .container { padding: 0 16px; }
}