@import url('https://fonts.googleapis.com/css2?family=Source+Serif+4:opsz,wght@8..60,400;8..60,600;8..60,700&family=IBM+Plex+Sans:wght@400;500;600&family=IBM+Plex+Mono:wght@400;500&display=swap');

:root {
  --ink: #1B2A4A;
  --ink-soft: #34456B;
  --paper: #EFEEE6;
  --paper-line: #D9D6C8;
  --marigold: #E2932E;
  --marigold-dark: #9C5F14;
  --slate-teal: #2F6E68;
  --slate-teal-dark: #1D4844;
  --pen-red: #B8443A;
  --muted: #6E7488;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'IBM Plex Sans', sans-serif;
  line-height: 1.6;
}

.wrap { max-width: 880px; margin: 0 auto; padding: 0 24px; }

/* Header */
header.site {
  border-bottom: 1px solid var(--paper-line);
  padding: 20px 0;
}
header.site .wrap { display: flex; align-items: flex-start; justify-content: space-between; gap: 24px; flex-wrap: wrap; }
.brand {
  font-family: 'Source Serif 4', serif;
  font-weight: 700;
  font-size: 22px;
  letter-spacing: -0.01em;
}
.brand-mark { color: var(--marigold-dark); }
.brand-tagline {
  font-family: 'Source Serif 4', serif;
  font-style: italic;
  font-size: 13px;
  color: var(--ink-soft);
  margin: 2px 0 0;
}
.tag { font-family: 'IBM Plex Mono', monospace; font-size: 12px; color: var(--muted); white-space: nowrap; padding-top: 4px; }

/* Hero */
.hero { padding: 56px 0 40px; }
.hero .eyebrow {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 13px;
  color: var(--slate-teal-dark);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin: 0 0 12px;
}
.hero h1 {
  font-family: 'Source Serif 4', serif;
  font-weight: 700;
  font-size: 40px;
  line-height: 1.15;
  margin: 0 0 16px;
  max-width: 12ch;
}
.hero p.lede {
  font-size: 17px;
  color: var(--ink-soft);
  max-width: 52ch;
  margin: 0 0 28px;
}

/* Ruled panel — the notebook-page motif used for the demo module and catalog */
.ruled {
  background: #FFFFFF;
  border: 1px solid var(--paper-line);
  border-radius: 3px;
  position: relative;
}
.ruled::before {
  content: "";
  position: absolute;
  top: 0; bottom: 0; left: 56px;
  width: 1px;
  background: var(--pen-red);
  opacity: 0.25;
}

.demo-panel { padding: 28px 28px 24px 76px; margin-bottom: 48px; }
.demo-panel .panel-label {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 12px;
  color: var(--muted);
  margin: 0 0 18px;
}

button {
  font-family: 'IBM Plex Sans', sans-serif;
  font-size: 14px;
  font-weight: 500;
  padding: 9px 16px;
  border-radius: 3px;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  cursor: pointer;
}
button:hover { background: var(--ink); color: var(--paper); }
button.active { background: var(--ink); color: var(--paper); }

/* Catalog — presented as a table of contents, not a card grid */
.catalog-heading {
  font-family: 'Source Serif 4', serif;
  font-weight: 600;
  font-size: 22px;
  margin: 0 0 6px;
}
.catalog-sub { color: var(--muted); font-size: 14px; margin: 0 0 24px; }

.subject-block { margin-bottom: 8px; }
.subject-row {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 10px 0;
  border-bottom: 1px solid var(--paper-line);
  cursor: pointer;
}
.subject-row:hover .subject-name { color: var(--marigold-dark); }
.chevron {
  display: inline-block;
  font-size: 10px;
  color: var(--muted);
  transition: transform 0.15s ease;
}
.chevron.open { transform: rotate(90deg); }
.subject-name {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--slate-teal-dark);
}
.subject-count {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 12px;
  color: var(--muted);
  margin-left: auto;
  white-space: nowrap;
}
.subject-tree {
  margin: 4px 0 16px;
  padding-left: 20px;
  border-left: 1px solid var(--paper-line);
}
.chapter-name {
  font-size: 16px;
  font-weight: 600;
  margin: 14px 0 8px;
}

.topic-row {
  display: flex;
  align-items: baseline;
  gap: 16px;
  padding: 10px 0;
  border-bottom: 1px solid var(--paper-line);
  cursor: pointer;
}
.topic-row:hover .topic-title { color: var(--marigold-dark); }
.topic-no {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 13px;
  color: var(--muted);
  width: 40px;
  flex: none;
}
.topic-main { flex: 1; min-width: 0; }
.topic-title { font-weight: 500; }
.topic-blurb { font-size: 13px; color: var(--muted); margin-top: 2px; }
.badge {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 11px;
  padding: 3px 8px;
  border-radius: 999px;
  flex: none;
  white-space: nowrap;
}
.badge.tricky { background: #FBE9D3; color: var(--marigold-dark); }
.badge.demo { background: #DCEAE8; color: var(--slate-teal-dark); }

/* Signup */
.signup { padding: 40px 0 64px; }
.signup-panel { padding: 28px; }
.signup-panel h3 { font-family: 'Source Serif 4', serif; margin: 0 0 8px; font-size: 20px; }
.signup-panel p { color: var(--muted); font-size: 14px; margin: 0 0 16px; }
.signup-form { display: flex; gap: 10px; flex-wrap: wrap; }
.signup-form input {
  flex: 1;
  min-width: 200px;
  padding: 10px 12px;
  border: 1px solid var(--paper-line);
  border-radius: 3px;
  font-family: 'IBM Plex Sans', sans-serif;
  font-size: 14px;
}
.signup-form button { background: var(--marigold-dark); border-color: var(--marigold-dark); color: #fff; }
.signup-form button:hover { background: var(--ink); border-color: var(--ink); }
.confirm { font-size: 14px; color: var(--slate-teal-dark); margin-top: 12px; display: none; }

footer.site { border-top: 1px solid var(--paper-line); padding: 24px 0; }
footer.site .wrap { font-size: 12px; color: var(--muted); font-family: 'IBM Plex Mono', monospace; }

/* Topic detail overlay */
.overlay {
  display: none;
  position: fixed; inset: 0;
  background: rgba(27, 42, 74, 0.5);
  align-items: flex-start;
  justify-content: center;
  padding: 40px 20px;
  overflow-y: auto;
  z-index: 10;
}
.overlay.open { display: flex; }
.overlay-panel {
  background: #fff;
  max-width: 720px;
  width: 100%;
  border-radius: 4px;
  padding: 32px;
}
.overlay-panel .close-row { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: 4px; }
.overlay-panel .close-row button { border: none; background: none; font-size: 20px; padding: 0; color: var(--muted); }
.overlay-panel h2 { font-family: 'Source Serif 4', serif; margin: 4px 0 4px; }
.overlay-meta { font-family: 'IBM Plex Mono', monospace; font-size: 12px; color: var(--muted); margin-bottom: 20px; }
.placeholder-note {
  background: var(--paper);
  border: 1px dashed var(--paper-line);
  padding: 20px;
  font-size: 14px;
  color: var(--ink-soft);
  border-radius: 3px;
}

@media (max-width: 560px) {
  .hero h1 { font-size: 30px; max-width: none; }
  .demo-panel { padding: 24px 16px 20px 16px; }
  .demo-panel::before { display: none; }
}