/* Clean learning site shell */
:root {
  --bg: #fafafa;
  --paper: #ffffff;
  --ink: #111827;
  --muted: #6b7280;
  --line: #e5e7eb;
  --line-strong: #d1d5db;
  --accent: #2563eb;
  --accent-soft: #eff6ff;
  --radius: 14px;
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans SC", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.6;
  font-size: 16px;
}
a { color: inherit; }
.site-header, .site-main, .site-footer {
  width: min(960px, calc(100% - 32px));
  margin-inline: auto;
}
.site-header {
  height: 64px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--line);
}
.brand {
  color: var(--ink);
  text-decoration: none;
  font-weight: 650;
  letter-spacing: -0.01em;
}
.brand-mark { display: none; }
.nav-links {
  display: flex;
  gap: 18px;
  font-size: 14px;
}
.nav-links a {
  color: var(--muted);
  text-decoration: none;
}
.nav-links a:hover { color: var(--ink); }
.hero {
  padding: 42px 0 24px;
  border-bottom: 1px solid var(--line);
}
.hero-panel { display: none; }
.kicker {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 14px;
  font-weight: 500;
}
h1 {
  margin: 0;
  font-size: clamp(2rem, 5vw, 3.25rem);
  line-height: 1.08;
  letter-spacing: -0.045em;
  font-weight: 720;
}
.hero-copy {
  margin: 12px 0 0;
  max-width: 64ch;
  color: var(--muted);
  font-size: 17px;
}
.toolbar {
  margin: 24px 0;
  display: flex;
  gap: 8px;
  align-items: center;
}
.search {
  flex: 1;
  min-width: 0;
  height: 42px;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--paper);
  color: var(--ink);
  padding: 0 12px;
  font: inherit;
  outline: none;
}
.search:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-soft);
}
.filter, .pill {
  height: 42px;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--paper);
  color: var(--muted);
  padding: 0 12px;
  font: inherit;
  font-size: 14px;
  text-decoration: none;
}
.filter { cursor: pointer; }
.filter[aria-pressed="true"] {
  color: var(--accent);
  border-color: #bfdbfe;
  background: var(--accent-soft);
}
.course-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}
.course-card {
  display: block;
  min-height: 178px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  background: var(--paper);
  color: var(--ink);
  text-decoration: none;
  transition: border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
.course-card:hover {
  border-color: var(--line-strong);
  transform: translateY(-1px);
  box-shadow: 0 8px 24px rgba(17, 24, 39, .06);
}
.course-card::after { display: none; }
.course-card h2 {
  margin: 0 0 8px;
  font-size: 22px;
  line-height: 1.25;
  letter-spacing: -0.02em;
}
.course-card p {
  margin: 0;
  color: var(--muted);
  font-size: 15px;
}
.meta-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 20px;
}
.meta-row span {
  color: var(--muted);
  background: #f9fafb;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 4px 8px;
  font-size: 12px;
}
.section-title {
  margin: 36px 0 12px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}
.section-title h2 {
  margin: 0;
  font-size: 20px;
  letter-spacing: -0.02em;
}
.lesson-list {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.lesson-item a {
  display: grid;
  grid-template-columns: 76px 1fr auto;
  gap: 12px;
  align-items: center;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--paper);
  color: var(--ink);
  text-decoration: none;
}
.lesson-item a:hover {
  border-color: var(--line-strong);
  background: #fcfcfd;
}
.lesson-num {
  color: var(--muted);
  font-size: 13px;
  font-variant-numeric: tabular-nums;
}
.lesson-arrow { color: var(--muted); }
.site-footer {
  color: var(--muted);
  padding: 40px 0 28px;
  font-size: 14px;
}
.empty {
  display: none;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px;
  background: var(--paper);
  color: var(--muted);
}
@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; transition: none !important; }
}
@media (max-width: 700px) {
  .site-header { height: 56px; }
  .nav-links { gap: 12px; }
  .hero { padding: 28px 0 18px; }
  .hero-copy { font-size: 16px; }
  .toolbar { align-items: stretch; flex-wrap: wrap; }
  .search { flex-basis: 100%; }
  .filter { flex: 1; }
  .course-grid { grid-template-columns: 1fr; }
  .course-card { min-height: 0; }
  .lesson-item a { grid-template-columns: 1fr auto; }
  .lesson-num { grid-column: 1 / -1; }
  .pill { display: none; }
}