:root {
  --bg: #07111f;
  --bg-accent: #10213c;
  --panel: rgba(10, 20, 38, 0.86);
  --panel-strong: rgba(16, 29, 52, 0.96);
  --border: rgba(151, 187, 255, 0.2);
  --border-strong: rgba(151, 187, 255, 0.34);
  --text: #eef4ff;
  --muted: #b2c3e3;
  --accent: #86c6ff;
  --accent-2: #b494ff;
  --accent-3: #7ef0d5;
  --shadow: 0 24px 80px rgba(0, 0, 0, 0.38);
  --radius-xl: 28px;
  --radius-lg: 20px;
  --radius-md: 14px;
  --max: 1120px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background:
    radial-gradient(circle at top left, rgba(97, 171, 255, 0.2), transparent 30%),
    radial-gradient(circle at top right, rgba(180, 148, 255, 0.16), transparent 26%),
    linear-gradient(180deg, var(--bg) 0%, #091523 100%);
}

a {
  color: inherit;
}

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

.page-shell {
  width: min(calc(100% - 32px), var(--max));
  margin: 0 auto;
  padding: 28px 0 64px;
}

.site-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  margin-bottom: 28px;
}

.brand,
.nav-links {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.brand {
  text-decoration: none;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.brand-mark,
.lesson-number {
  display: inline-grid;
  place-items: center;
  width: 40px;
  height: 40px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: linear-gradient(135deg, rgba(134, 198, 255, 0.22), rgba(180, 148, 255, 0.18));
  box-shadow: var(--shadow);
}

.nav-pill,
.button,
.check-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 44px;
  padding: 0 16px;
  border-radius: 999px;
  text-decoration: none;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.05);
  color: var(--text);
  transition: transform 160ms ease, border-color 160ms ease, background 160ms ease;
}

.nav-pill:hover,
.button:hover,
.check-toggle:hover {
  transform: translateY(-1px);
  border-color: var(--border-strong);
  background: rgba(255, 255, 255, 0.08);
}

.button.primary {
  background: linear-gradient(135deg, rgba(134, 198, 255, 0.22), rgba(126, 240, 213, 0.16));
  border-color: rgba(126, 240, 213, 0.32);
}

.hero,
.lesson-hero,
.card,
.side-card,
.checklist,
.resources,
.footer-card,
.progress-banner {
  border: 1px solid var(--border);
  background: var(--panel);
  backdrop-filter: blur(14px);
  box-shadow: var(--shadow);
}

.hero,
.lesson-hero {
  border-radius: var(--radius-xl);
  overflow: hidden;
  position: relative;
}

.hero-grid,
.lesson-grid,
.footer-grid,
.lesson-layout {
  display: grid;
  gap: 22px;
}

.hero-grid {
  grid-template-columns: minmax(0, 1.2fr) minmax(280px, 0.8fr);
  padding: 34px;
}

.lesson-grid {
  grid-template-columns: minmax(0, 1.1fr) minmax(290px, 0.9fr);
  padding: 30px;
}

.eyebrow {
  margin: 0 0 14px;
  font-size: 0.78rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 700;
}

h1,
h2,
h3 {
  margin: 0;
  letter-spacing: -0.03em;
}

h1 {
  font-size: clamp(2.4rem, 5vw, 4.7rem);
  line-height: 0.96;
}

h2 {
  font-size: clamp(1.5rem, 3vw, 2.2rem);
  line-height: 1.05;
}

h3 {
  font-size: 1.12rem;
  line-height: 1.15;
}

.hero-copy,
.lead,
.card p,
.side-card p,
.resources li,
.checklist li,
.footer-card p,
.lesson-intro,
.note {
  color: var(--muted);
  line-height: 1.7;
}

.hero-copy,
.lesson-intro {
  font-size: 1.06rem;
  max-width: 42rem;
}

.hero-actions,
.meta-row,
.lesson-meta,
.button-row,
.resource-links,
.status-row {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.meta-chip,
.status-chip {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 8px 12px;
  background: rgba(255,255,255,0.05);
  color: var(--muted);
  font-size: 0.92rem;
}

.toc-grid,
.lesson-cards,
.footer-grid {
  display: grid;
  gap: 18px;
}

.toc-grid {
  margin-top: 24px;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}

.card,
.side-card,
.checklist,
.resources,
.footer-card,
.progress-banner {
  border-radius: var(--radius-lg);
  padding: 22px;
}

.card {
  text-decoration: none;
  display: flex;
  flex-direction: column;
  gap: 14px;
  min-height: 250px;
  transition: transform 160ms ease, border-color 160ms ease;
}

.card:hover {
  transform: translateY(-3px);
  border-color: var(--border-strong);
}

.card-top,
.lesson-card-top {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 14px;
}

.card-icon,
.lesson-icon {
  width: 50px;
  height: 50px;
  border-radius: 16px;
  display: inline-grid;
  place-items: center;
  font-size: 1.4rem;
  background: rgba(255,255,255,0.06);
  border: 1px solid rgba(255,255,255,0.08);
}

.card ul,
.checklist ul,
.resources ul,
.footer-card ul {
  margin: 0;
  padding-left: 18px;
}

.card li,
.checklist li,
.resources li,
.footer-card li {
  margin-top: 8px;
}

.progress-banner {
  margin-top: 22px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
}

.progress-copy strong {
  display: block;
  margin-bottom: 4px;
}

.progress-meter {
  width: min(320px, 100%);
  height: 12px;
  border-radius: 999px;
  overflow: hidden;
  background: rgba(255,255,255,0.08);
  border: 1px solid rgba(255,255,255,0.08);
}

.progress-meter > span {
  display: block;
  height: 100%;
  width: 0;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--accent), var(--accent-3));
  transition: width 220ms ease;
}

.section-title {
  margin: 34px 0 14px;
}

.lesson-layout {
  margin-top: 28px;
  grid-template-columns: minmax(0, 1.15fr) minmax(270px, 0.85fr);
  align-items: start;
}

.lesson-main {
  display: grid;
  gap: 18px;
}

.lesson-sidebar {
  display: grid;
  gap: 18px;
  position: sticky;
  top: 18px;
}

.lesson-nav {
  margin-top: 12px;
  display: flex;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.lesson-nav .button {
  flex: 1 1 180px;
}

.check-toggle {
  width: 100%;
  font: inherit;
  cursor: pointer;
}

.check-toggle[aria-pressed="true"] {
  background: linear-gradient(135deg, rgba(126, 240, 213, 0.22), rgba(134, 198, 255, 0.16));
  border-color: rgba(126, 240, 213, 0.34);
}

.resource-links a {
  text-decoration: none;
}

.footer-grid {
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  margin-top: 28px;
}

footer {
  margin-top: 34px;
}

.small {
  font-size: 0.94rem;
}

.muted {
  color: var(--muted);
}

@media (max-width: 900px) {
  .hero-grid,
  .lesson-grid,
  .lesson-layout {
    grid-template-columns: 1fr;
  }

  .lesson-sidebar {
    position: static;
  }
}

@media (max-width: 640px) {
  .page-shell {
    width: min(calc(100% - 20px), var(--max));
    padding-top: 18px;
    padding-bottom: 44px;
  }

  .hero-grid,
  .lesson-grid,
  .card,
  .side-card,
  .checklist,
  .resources,
  .footer-card,
  .progress-banner {
    padding: 18px;
  }

  h1 {
    font-size: clamp(2rem, 11vw, 3rem);
  }
}