/* ============================================================================
   Chapter 5 — B+ tree interactives
   ========================================================================== */

.invariant-panel {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(12rem, 1fr));
  gap: .8rem;
  padding: 1rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow-sm);
}
.mbr { display: none; }
.inv-card {
  min-height: 10.5rem;
  padding: 1rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
}
.inv-card b {
  display: inline-grid;
  place-items: center;
  width: 1.7rem;
  height: 1.7rem;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  font-family: var(--font-mono);
  font-size: .82rem;
  margin-bottom: .8rem;
}
.inv-card span { display: block; font-weight: 750; line-height: 1.35; }
.inv-card p { margin: .5rem 0 0; font-size: .84rem; line-height: 1.55; color: var(--ink-faint); }

/* ---------- B+ tree sandbox ---------- */
.bt-shell { display: grid; gap: 1rem; }
.bt-controls {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: .9rem;
  align-items: start;
}
.bt-control-group {
  display: flex;
  flex-wrap: wrap;
  gap: .5rem;
  align-items: center;
}
.bt-control-group label,
.calc-row label,
.trade-row label {
  font-size: .76rem;
  font-weight: 700;
  color: var(--ink-faint);
  letter-spacing: .08em;
  text-transform: uppercase;
}
.bt-input {
  width: 5.5rem;
  height: 2.25rem;
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font-family: var(--font-mono);
  padding: .35rem .55rem;
}
.bt-range-input { width: 4.6rem; }
.bt-demo { justify-content: flex-end; }
.bt-demo .btn { white-space: nowrap; }

.bt-stats {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: .6rem;
}
.bt-stat {
  min-height: 4.1rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
  padding: .65rem .75rem;
}
.bt-stat b {
  display: block;
  font-family: var(--font-serif);
  font-size: 1.35rem;
  line-height: 1;
  color: var(--accent);
}
.bt-stat span {
  display: block;
  margin-top: .25rem;
  color: var(--ink-faint);
  font-size: .72rem;
}

.bt-stage {
  width: 100%;
  max-width: 100%;
  min-height: 24rem;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
  background:
    linear-gradient(var(--surface), var(--surface)) padding-box,
    repeating-linear-gradient(90deg, transparent 0, transparent 35px, var(--line) 36px) border-box;
  padding: 1.3rem;
}
.bt-levels {
  min-width: 42rem;
  display: grid;
  gap: 1.15rem;
}
.bt-level {
  display: flex;
  justify-content: center;
  gap: .9rem;
  min-height: 4.75rem;
  align-items: center;
  position: relative;
}
.bt-level-label {
  width: 4.6rem;
  flex: none;
  align-self: stretch;
  display: grid;
  place-items: center;
  color: var(--ink-faint);
  font-family: var(--font-mono);
  font-size: .7rem;
}
.bt-level-nodes {
  flex: 1;
  display: flex;
  justify-content: center;
  gap: .9rem;
  align-items: center;
}
.bt-node {
  min-width: 7.5rem;
  max-width: 13rem;
  border: 1.5px solid var(--line-strong);
  border-radius: 8px;
  background: var(--surface);
  box-shadow: var(--shadow-sm);
  transition: border-color .18s, transform .18s, background .18s, box-shadow .18s;
}
.bt-node.hot {
  border-color: var(--accent);
  background: var(--accent-wash);
  box-shadow: 0 0 0 4px var(--accent-wash), var(--shadow-sm);
}
.bt-node.changed {
  border-color: var(--warm);
  background: var(--warm-wash);
}
.bt-node.range-hit { border-color: var(--good); background: var(--good-wash); }
.bt-node-head {
  display: flex;
  justify-content: space-between;
  gap: .6rem;
  border-bottom: 1px solid var(--line);
  padding: .42rem .55rem;
  font-size: .66rem;
  color: var(--ink-faint);
  text-transform: uppercase;
  letter-spacing: .08em;
  font-weight: 750;
}
.bt-node-body {
  display: flex;
  flex-wrap: wrap;
  gap: .28rem;
  padding: .65rem;
  min-height: 3.1rem;
  align-items: center;
  justify-content: center;
}
.bt-key {
  min-width: 2.05rem;
  height: 1.8rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0 .35rem;
  border-radius: 6px;
  background: var(--surface-2);
  border: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: .82rem;
  color: var(--ink);
}
.bt-key.hit { background: var(--warm); color: #fff; border-color: var(--warm); }
.bt-key.range { background: var(--good); color: #fff; border-color: var(--good); }

.leaf-chain {
  width: 100%;
  max-width: 100%;
  display: flex;
  align-items: center;
  gap: .45rem;
  padding: .75rem .8rem;
  border: 1px dashed var(--line-strong);
  border-radius: 8px;
  background: var(--surface-2);
  overflow-x: auto;
}
.leaf-chip {
  display: inline-flex;
  gap: .25rem;
  align-items: center;
  white-space: nowrap;
  font-family: var(--font-mono);
  font-size: .76rem;
  padding: .28rem .45rem;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--surface);
}
.leaf-chip.hit { border-color: var(--good); background: var(--good-wash); }
.leaf-arrow { color: var(--ink-faint); font-family: var(--font-mono); }

.bt-log {
  min-height: 7.5rem;
  max-height: 12rem;
  overflow: auto;
  padding: .85rem 1rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
  font-family: var(--font-mono);
  font-size: .75rem;
  line-height: 1.6;
}
.bt-log div { border-bottom: 1px solid var(--line); padding: .28rem 0; }
.bt-log div:last-child { border-bottom: none; }
.bt-log .op { color: var(--accent); font-weight: 750; }
.bt-log .warn { color: var(--warm); }
.bt-log .ok { color: var(--good); }

/* ---------- calculators ---------- */
.calc-grid,
.trade-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(16rem, .95fr);
  gap: 1.2rem;
  align-items: stretch;
}
.calc-controls,
.trade-controls {
  display: grid;
  gap: .9rem;
}
.calc-row,
.trade-row {
  display: grid;
  grid-template-columns: 8.5rem minmax(8rem, 1fr) 5.5rem;
  gap: .8rem;
  align-items: center;
}
.calc-row output,
.trade-row output {
  font-family: var(--font-mono);
  font-size: .82rem;
  color: var(--accent);
  text-align: right;
}
.calc-result,
.trade-result {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
  padding: 1rem;
}
.big-number {
  font-family: var(--font-serif);
  font-size: 3rem;
  line-height: .95;
  color: var(--accent);
}
.calc-metrics {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: .6rem;
  margin-top: 1rem;
}
.calc-metric {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  padding: .65rem;
}
.calc-metric b { display: block; font-family: var(--font-mono); color: var(--ink); }
.calc-metric span { display: block; color: var(--ink-faint); font-size: .75rem; margin-top: .15rem; }
.height-bars { display: flex; align-items: end; gap: .35rem; height: 6.8rem; margin-top: 1rem; }
.height-bar {
  flex: 1;
  border-radius: 6px 6px 0 0;
  background: linear-gradient(180deg, var(--accent), var(--accent-wash));
  min-height: .6rem;
  border: 1px solid var(--line);
}

.trade-bars { display: grid; gap: .7rem; margin: 1rem 0; }
.trade-bar {
  height: 1rem;
  border-radius: 999px;
  background: var(--surface);
  border: 1px solid var(--line);
  overflow: hidden;
}
.trade-bar span {
  display: block;
  height: 100%;
  width: 50%;
  background: linear-gradient(90deg, var(--accent), var(--warm));
}
.trade-side {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: .7rem;
}
.trade-card {
  min-height: 9rem;
  padding: .85rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
}
.trade-card b { display: block; color: var(--ink); }
.trade-card p { margin: .5rem 0 0; font-size: .82rem; line-height: 1.55; color: var(--ink-faint); }
.trade-verdict {
  margin-top: .9rem;
  padding: .75rem .85rem;
  border-left: 3px solid var(--accent);
  border-radius: 0 8px 8px 0;
  background: var(--accent-wash);
  color: var(--ink-soft);
  font-size: .9rem;
  line-height: 1.55;
}

@media (max-width: 820px) {
  .mbr { display: block; }
  .ch-title { overflow-wrap: anywhere; }
  .bt-controls,
  .calc-grid,
  .trade-grid,
  .trade-side { grid-template-columns: 1fr; }
  .bt-demo { justify-content: flex-start; }
  .bt-stats { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .calc-row,
  .trade-row { grid-template-columns: 1fr; gap: .35rem; }
  .calc-row output,
  .trade-row output { text-align: left; }
}