:root {
  --navy: #0f2744;
  --navy-2: #173456;
  --ink: #1b2430;
  --muted: #5c6777;
  --line: #e2e6ec;
  --paper: #f6f3ec;
  --card: #ffffff;
  --gold: #b0892e;
  --gold-2: #c4a35a;
  --moss: #2f6f56;
  --fail: #9b2c2c;
  --sans: "IBM Plex Sans", "Segoe UI", sans-serif;
  --serif: "IBM Plex Serif", Georgia, serif;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
}

* { box-sizing: border-box; }
html, body { margin: 0; min-height: 100%; }
body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16.5px;
  line-height: 1.55;
}

.skip { position: absolute; left: -999px; }
.skip:focus { left: 12px; top: 12px; background: #fff; padding: 8px; z-index: 40; }

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 16px;
  min-height: 64px;
  padding: 0 22px;
  background: var(--navy);
  color: #f4efe4;
  border-bottom: 1px solid rgba(196, 163, 90, 0.35);
}
.brand { display: flex; align-items: center; gap: 12px; color: inherit; text-decoration: none; min-width: 0; }
.brand-mark {
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  border: 1px solid var(--gold-2);
  font-family: var(--serif);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--gold-2);
}
.brand-text { display: grid; line-height: 1.15; }
.brand-text strong { font-family: var(--serif); font-size: 16px; font-weight: 600; }
.brand-text em { font-style: normal; font-size: 12px; color: #c5d0de; }
.top-actions { margin-left: auto; display: flex; align-items: center; gap: 8px; }
.top-link, .search-btn, .menu-btn {
  color: #e8eef6;
  background: transparent;
  border: 1px solid rgba(255,255,255,0.16);
  text-decoration: none;
  font: 500 13px var(--sans);
  padding: 7px 11px;
  cursor: pointer;
}
.top-link:hover, .search-btn:hover, .menu-btn:hover { border-color: var(--gold-2); color: #fff; }
.search-btn kbd {
  font-family: var(--mono);
  font-size: 10px;
  border: 1px solid rgba(255,255,255,0.25);
  padding: 0 4px;
  margin-left: 6px;
}
.menu-btn { display: none; }

.shell {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr);
  min-height: calc(100vh - 64px);
}
.spine {
  background: #fbfaf6;
  border-right: 1px solid var(--line);
  padding: 22px 16px 28px;
  position: sticky;
  top: 64px;
  height: calc(100vh - 64px);
  overflow: auto;
}
.nav { display: grid; gap: 2px; }
.nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  padding: 7px 10px;
  border-left: 2px solid transparent;
}
.nav a:hover, .nav a.active {
  color: var(--navy);
  border-left-color: var(--gold);
  background: #fff;
}
.spine-label {
  margin: 22px 10px 8px;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--gold);
}
.spine-plates { list-style: none; margin: 0; padding: 0; }
.spine-plates a {
  display: grid;
  grid-template-columns: 18px 1fr;
  gap: 8px;
  align-items: center;
  color: var(--muted);
  text-decoration: none;
  font-size: 13px;
  padding: 6px 8px;
}
.spine-plates .dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  border: 1px solid var(--gold-2);
  background: #fff;
}
.spine-plates a.done .dot { background: var(--moss); border-color: var(--moss); }
.spine-plates a:hover { color: var(--navy); }
.spine-foot { margin: 24px 10px 0; font-size: 12px; color: var(--muted); line-height: 1.4; }

.view { padding: 36px 48px 88px; max-width: 980px; }
.kicker {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--gold);
  margin: 0 0 10px;
}
h1, h2, h3 { font-family: var(--serif); font-weight: 600; color: var(--navy); letter-spacing: -0.02em; }
h1 { font-size: clamp(1.9rem, 3.4vw, 2.7rem); line-height: 1.15; margin: 0 0 14px; }
h2 { font-size: 1.35rem; margin: 1.7em 0 0.45em; }
h3 { font-size: 1.08rem; margin: 1.2em 0 0.35em; }
.lede { font-size: 1.08rem; color: var(--muted); max-width: 42rem; }

.metrics {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
  margin: 28px 0 8px;
}
.metric {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 14px 16px;
}
.metric b {
  display: block;
  font-family: var(--serif);
  font-size: 1.6rem;
  color: var(--navy);
}
.metric span { font-size: 12px; color: var(--muted); }

.actions { display: flex; flex-wrap: wrap; gap: 10px; margin: 22px 0 10px; }
.btn {
  appearance: none;
  border: 1px solid var(--navy);
  background: var(--navy);
  color: #f7f4ee;
  font: 600 13.5px var(--sans);
  padding: 10px 16px;
  cursor: pointer;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
}
.btn.ghost { background: transparent; color: var(--navy); }
.btn:hover { background: #173456; color: #fff; }
.btn.ghost:hover { background: var(--navy); color: #fff; }
.btn:disabled, .btn:disabled:hover {
  opacity: 0.35;
  cursor: not-allowed;
  background: var(--navy);
  color: #f7f4ee;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
  gap: 12px;
  margin-top: 24px;
}
.card {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 16px;
  text-decoration: none;
  color: inherit;
  display: grid;
  gap: 8px;
  min-height: 132px;
}
.card:hover { border-color: var(--navy); }
.card .n { font-family: var(--mono); font-size: 11px; color: var(--gold); letter-spacing: 0.04em; }
.card h3 { margin: 0; }
.card p { margin: 0; color: var(--muted); font-size: 14px; }

.metro { margin-top: 12px; }
.metro-row {
  display: grid;
  grid-template-columns: 64px 1fr auto;
  gap: 16px;
  align-items: center;
  text-decoration: none;
  color: inherit;
  padding: 16px 4px;
  border-top: 1px solid var(--line);
  background: transparent;
}
.metro-row:hover h3 { color: var(--gold); }
.metro-num { font-family: var(--serif); font-size: 26px; color: var(--gold); }
.chip {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  border: 1px solid var(--line);
  padding: 3px 7px;
}

.progress-bar { height: 6px; background: #e8e4da; margin-top: 16px; }
.progress-bar > span { display: block; height: 100%; background: var(--moss); }

.lesson { max-width: 44rem; }
.lesson h1 { font-size: 2rem; }
.toc {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 12px 16px;
  margin: 0 0 24px;
  font-size: 14px;
}
.toc a { color: var(--navy); }
.lesson code, :not(pre) > code {
  font-family: var(--mono);
  font-size: 0.86em;
  background: #ece7dc;
  padding: 0.08em 0.32em;
}
.lesson pre {
  background: var(--navy);
  color: #f3ead8;
  padding: 14px 16px;
  overflow: auto;
  font-family: var(--mono);
  font-size: 13px;
}
.lesson pre code { background: none; color: inherit; padding: 0; }
.lesson table { border-collapse: collapse; width: 100%; font-size: 14.5px; margin: 1em 0; }
.lesson th, .lesson td { border: 1px solid var(--line); padding: 7px 8px; text-align: left; }
.lesson blockquote { margin: 1em 0; padding-left: 14px; border-left: 3px solid var(--gold); color: var(--muted); }
.lesson a { color: #1e4d7b; }

.quiz-meta { display: flex; flex-wrap: wrap; gap: 12px; font-family: var(--mono); font-size: 12px; color: var(--muted); }
.choice {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: 10px;
  width: 100%;
  text-align: left;
  border: 1px solid var(--line);
  background: var(--card);
  padding: 12px 14px;
  margin: 8px 0;
  cursor: pointer;
  font: 400 16px var(--sans);
  color: var(--ink);
}
.choice:hover { border-color: var(--navy); }
.choice .letter { font-family: var(--mono); color: var(--gold); }
.choice.correct { border-color: var(--moss); background: #eef6f1; }
.choice.wrong { border-color: var(--fail); background: #f8eceb; }
.explain { background: var(--card); border: 1px solid var(--line); padding: 12px 14px; margin: 12px 0; }
.score-hero { font-family: var(--serif); font-size: 4rem; margin: 4px 0 8px; color: var(--navy); }
.pass { color: var(--moss); }
.fail { color: var(--fail); }

.crumbs { font-size: 13px; color: var(--muted); margin-bottom: 16px; }
.crumbs a { color: inherit; }
.err { color: var(--fail); }

.faq details {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 12px 16px;
  margin: 8px 0;
}
.faq summary { cursor: pointer; font-weight: 600; color: var(--navy); }
.term {
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: 16px;
  padding: 12px 0;
  border-top: 1px solid var(--line);
}
.term b { color: var(--navy); }

.search-scrim {
  position: fixed;
  inset: 0;
  background: rgba(15, 39, 68, 0.45);
  z-index: 30;
  display: grid;
  place-items: start center;
  padding-top: 12vh;
}
.search-scrim[hidden] { display: none !important; }
.search-scrim[hidden] { display: none !important; }
.search-panel {
  width: min(640px, calc(100% - 24px));
  background: #fff;
  border: 1px solid var(--navy);
  padding: 12px;
}
.search-panel input {
  width: 100%;
  border: 1px solid var(--line);
  font: 400 16px var(--sans);
  padding: 10px 12px;
}
.search-hit {
  display: block;
  padding: 10px 8px;
  color: inherit;
  text-decoration: none;
  border-top: 1px solid var(--line);
}
.search-hit:hover { background: var(--paper); }
.search-hit small { display: block; color: var(--muted); }
.search-hint { margin: 8px 4px 0; font-size: 12px; color: var(--muted); }

.week-row {
  display: grid;
  grid-template-columns: 72px 1fr 1.4fr;
  gap: 12px;
  padding: 10px 0;
  border-top: 1px solid var(--line);
  font-size: 14.5px;
}

@media (max-width: 900px) {
  .menu-btn { display: inline-flex; }
  .shell { grid-template-columns: 1fr; }
  .spine {
    display: none;
    position: static;
    height: auto;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }
  .spine.open { display: block; }
  .view { padding: 24px 18px 64px; }
  .metrics { grid-template-columns: 1fr 1fr; }
  .term, .week-row { grid-template-columns: 1fr; }
  .brand-text em { display: none; }
}