.lesson-story {
  --ls-bg: #080d15;
  --ls-surface: rgba(15, 23, 35, 0.82);
  --ls-surface-solid: #101824;
  --ls-border: rgba(148, 163, 184, 0.16);
  --ls-copy: #a9b5c5;
  --ls-muted: #718096;
  --ls-heading: #f7f9fc;
  --ls-accent: #78b7ff;
  --ls-accent-strong: #b8d8ff;
  --ls-accent-rgb: 120, 183, 255;
  --ls-second: #66d9b7;
  --ls-code: #b9d8f4;
  --ls-code-output: #bce4c8;
  --ls-on-accent: #071019;
  --ls-danger: #ffb0a7;
  --ls-success-soft: #9be0cb;
  --ls-info-soft: #b8d8ff;
  position: relative;
  isolation: isolate;
  overflow: hidden;
  border: 1px solid var(--ls-border);
  border-radius: 2.25rem;
  color: var(--ls-copy);
  background:
    radial-gradient(circle at 50% 0%, rgba(var(--ls-accent-rgb), 0.12), transparent 34rem),
    linear-gradient(180deg, #0b121d 0%, var(--ls-bg) 46%, #090f18 100%);
  box-shadow: 0 34px 90px rgba(0, 0, 0, 0.3);
}

.lesson-story--btree {
  --ls-accent: #66d9b7;
  --ls-accent-strong: #b6f2df;
  --ls-accent-rgb: 102, 217, 183;
  --ls-second: #78b7ff;
}

.lesson-story--vacuum {
  --ls-accent: #efbd69;
  --ls-accent-strong: #ffe1a6;
  --ls-accent-rgb: 239, 189, 105;
  --ls-second: #69d0ad;
}

.lesson-story--locks {
  --ls-accent: #ff978c;
  --ls-accent-strong: #ffd0ca;
  --ls-accent-rgb: 255, 151, 140;
  --ls-second: #9ea8ff;
}

.lesson-story button {
  -webkit-tap-highlight-color: transparent;
}

.lesson-story button:focus-visible,
.lesson-story summary:focus-visible,
.lesson-story a:focus-visible {
  outline: 2px solid var(--ls-accent);
  outline-offset: 3px;
}

.ls-aurora {
  pointer-events: none;
  position: absolute;
  z-index: -1;
  border-radius: 999px;
  filter: blur(90px);
  opacity: 0.17;
}

.ls-aurora--one {
  top: 11rem;
  left: -10rem;
  width: 28rem;
  height: 28rem;
  background: var(--ls-accent);
}

.ls-aurora--two {
  top: 68rem;
  right: -12rem;
  width: 34rem;
  height: 34rem;
  background: var(--ls-second);
}

.ls-intro {
  padding: 4.5rem 2rem 4rem;
  text-align: center;
}

.ls-eyebrow,
.ls-chapter-number {
  color: var(--ls-accent);
  font-size: 0.74rem;
  font-weight: 750;
  letter-spacing: 0.2em;
  text-transform: uppercase;
}

.ls-intro h2 {
  max-width: 48rem;
  margin: 0.9rem auto 0;
  color: var(--ls-heading);
  font-size: clamp(2.2rem, 6vw, 4.45rem);
  font-weight: 620;
  letter-spacing: -0.05em;
  line-height: 1.01;
}

.ls-intro > p:last-child {
  max-width: 40rem;
  margin: 1.4rem auto 0;
  font-size: 1rem;
  line-height: 1.75;
}

.ls-chapter {
  position: relative;
  padding: 4.75rem 2rem;
  border-top: 1px solid var(--ls-border);
}

.ls-chapter-copy {
  max-width: 39rem;
}

.ls-chapter-copy h3 {
  margin-top: 0.75rem;
  color: var(--ls-heading);
  font-size: clamp(1.75rem, 4vw, 2.8rem);
  font-weight: 620;
  letter-spacing: -0.04em;
  line-height: 1.1;
}

.ls-chapter-copy > p:last-child {
  margin-top: 1rem;
  font-size: 0.95rem;
  line-height: 1.75;
}

.ls-story-heading {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 2rem;
  margin-top: 2.5rem;
}

.ls-live-copy {
  max-width: 42rem;
  min-height: 7rem;
}

.ls-live-copy > p {
  color: var(--ls-accent);
  font-size: 0.72rem;
  font-weight: 750;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.ls-live-copy h4 {
  margin-top: 0.45rem;
  color: var(--ls-heading);
  font-size: 1.18rem;
  font-weight: 650;
}

.ls-live-copy > div {
  margin-top: 0.55rem;
  color: var(--ls-copy);
  font-size: 0.9rem;
  line-height: 1.72;
}

.ls-play {
  display: inline-flex;
  min-height: 2.75rem;
  flex: none;
  align-items: center;
  gap: 0.65rem;
  padding: 0.6rem 1rem;
  border: 1px solid rgba(var(--ls-accent-rgb), 0.35);
  border-radius: 999px;
  color: var(--ls-accent-strong);
  background: rgba(var(--ls-accent-rgb), 0.08);
  font-size: 0.78rem;
  font-weight: 700;
  cursor: pointer;
  transition:
    border-color 180ms ease,
    background 180ms ease,
    transform 180ms ease;
}

.ls-play:hover {
  border-color: rgba(var(--ls-accent-rgb), 0.7);
  background: rgba(var(--ls-accent-rgb), 0.14);
  transform: translateY(-1px);
}

.ls-play span {
  display: grid;
  width: 1.45rem;
  height: 1.45rem;
  place-items: center;
  border-radius: 50%;
  color: var(--ls-on-accent);
  background: var(--ls-accent);
  font-size: 0.68rem;
}

.ls-step-controls {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin-top: 1rem;
  overflow: hidden;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(8, 13, 21, 0.55);
}

.ls-step-controls button {
  display: flex;
  min-height: 3.7rem;
  align-items: center;
  justify-content: center;
  gap: 0.55rem;
  border: 0;
  border-right: 1px solid var(--ls-border);
  color: var(--ls-muted);
  background: transparent;
  font-size: 0.78rem;
  cursor: pointer;
  transition:
    color 180ms ease,
    background 180ms ease;
}

.ls-step-controls button:last-child {
  border-right: 0;
}

.ls-step-controls button span:first-child {
  display: grid;
  width: 1.4rem;
  height: 1.4rem;
  place-items: center;
  border-radius: 50%;
  background: rgba(148, 163, 184, 0.1);
  font-size: 0.7rem;
  font-weight: 700;
}

.ls-step-controls button[data-selected="true"] {
  color: var(--ls-heading);
  background: rgba(var(--ls-accent-rgb), 0.1);
}

.ls-step-controls button[data-selected="true"] span:first-child {
  color: var(--ls-on-accent);
  background: var(--ls-accent);
}

.ls-memory {
  max-width: 48rem;
  margin: 1.7rem auto 0;
  color: var(--ls-copy);
  font-size: 0.9rem;
  line-height: 1.72;
  text-align: center;
}

.ls-memory strong {
  color: var(--ls-heading);
}

.ls-segmented {
  display: grid;
  max-width: 46rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin-top: 2.5rem;
  padding: 0.3rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(8, 13, 21, 0.7);
}

.ls-segmented button {
  min-height: 3.4rem;
  padding: 0.65rem 0.8rem;
  border: 1px solid transparent;
  border-radius: 0.75rem;
  color: var(--ls-muted);
  background: transparent;
  font-size: 0.7rem;
  font-weight: 650;
  cursor: pointer;
}

.ls-segmented button[data-selected="true"] {
  border-color: rgba(var(--ls-accent-rgb), 0.3);
  color: var(--ls-accent-strong);
  background: rgba(var(--ls-accent-rgb), 0.1);
}

.ls-rule {
  display: flex;
  max-width: 48rem;
  align-items: center;
  gap: 1.25rem;
  margin: 1.5rem auto 0;
  padding: 1rem 1.25rem;
  border: 1px solid rgba(var(--ls-accent-rgb), 0.16);
  border-radius: 1rem;
  background: rgba(var(--ls-accent-rgb), 0.055);
}

.ls-rule > span {
  flex: none;
  color: var(--ls-accent);
  font-size: 0.7rem;
  font-weight: 750;
  letter-spacing: 0.13em;
  text-transform: uppercase;
}

.ls-rule p {
  color: var(--ls-copy);
  font-size: 0.84rem;
  line-height: 1.68;
}

.ls-rule strong {
  color: var(--ls-heading);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-weight: 600;
}

.ls-rule b {
  padding-inline: 0.3rem;
  color: var(--ls-accent);
}

.ls-disclosure {
  border-top: 1px solid var(--ls-border);
  background: rgba(5, 9, 15, 0.3);
}

.ls-proof-disclosure {
  margin-top: 2.5rem;
  overflow: hidden;
  border: 1px solid var(--ls-border);
  border-radius: 1.25rem;
  background: rgba(8, 13, 21, 0.7);
}

.ls-proof-disclosure > summary:focus-visible {
  outline-offset: -4px;
}

.ls-disclosure summary {
  display: flex;
  min-height: 4.8rem;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.35rem;
  color: var(--ls-heading);
  font-size: 0.82rem;
  font-weight: 650;
  list-style: none;
  cursor: pointer;
}

.ls-disclosure summary::-webkit-details-marker {
  display: none;
}

.ls-disclosure summary small {
  display: block;
  margin-bottom: 0.25rem;
  color: var(--ls-accent);
  font-size: 0.7rem;
  font-weight: 750;
  letter-spacing: 0.13em;
  text-transform: uppercase;
}

.ls-disclosure-icon {
  display: grid;
  width: 2rem;
  height: 2rem;
  flex: none;
  place-items: center;
  border: 1px solid var(--ls-border);
  border-radius: 50%;
  color: var(--ls-muted);
  transition: transform 180ms ease;
}

.ls-disclosure[open] .ls-disclosure-icon {
  transform: rotate(45deg);
}

.ls-proof-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  border-top: 1px solid var(--ls-border);
}

.ls-proof-pane {
  min-width: 0;
  border-right: 1px solid var(--ls-border);
  background: rgba(13, 20, 31, 0.9);
}

.ls-proof-pane:last-child {
  border-right: 0;
}

.ls-proof-heading {
  display: flex;
  min-height: 3rem;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--ls-border);
  color: var(--ls-heading);
  font-size: 0.8rem;
  font-weight: 700;
}

.ls-proof-heading small {
  color: var(--ls-muted);
  font-size: 0.72rem;
  font-weight: 600;
}

.ls-copy {
  min-height: 2.75rem;
}

.ls-proof-pane pre {
  max-height: 27rem;
  margin: 0;
  overflow: auto;
  padding: 1rem;
  color: var(--ls-code);
  background: transparent;
  font-size: 0.8rem;
  line-height: 1.68;
  white-space: pre;
}

.ls-proof-pane pre code {
  padding: 0;
  color: inherit;
  background: transparent;
}

.ls-proof-output pre {
  color: var(--ls-code-output);
}

.ls-proof-payoff {
  padding: 1rem 1.25rem 1.25rem;
  border-top: 1px solid var(--ls-border);
  color: var(--ls-copy);
  font-size: 0.84rem;
  line-height: 1.72;
}

.ls-proof-payoff strong {
  color: var(--ls-accent);
}

.ls-source-trail summary {
  padding: 1.25rem 2rem;
}

.ls-call-path {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1px;
  margin: 0 2rem;
  overflow: hidden;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: var(--ls-border);
}

.ls-call-node {
  display: grid;
  min-width: 0;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 0.8rem;
  padding: 1rem;
  background: rgba(11, 17, 26, 0.95);
}

.ls-call-node > span {
  color: var(--ls-muted);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.68rem;
}

.ls-call-node strong {
  display: block;
  color: var(--ls-heading);
  font-size: 0.82rem;
}

.ls-call-node code {
  display: block;
  margin-top: 0.25rem;
  overflow-wrap: anywhere;
  color: var(--ls-accent);
  background: transparent;
  font-size: 0.72rem;
}

.ls-call-node p {
  margin-top: 0.6rem;
  color: var(--ls-muted);
  font-size: 0.76rem;
  line-height: 1.6;
}

.ls-guardrails {
  margin: 1.25rem 2rem 0;
  padding: 1.25rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(8, 13, 21, 0.48);
}

.ls-guardrails > p {
  color: var(--ls-accent);
  font-size: 0.7rem;
  font-weight: 750;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.ls-guardrails ul {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem 1.5rem;
  margin-top: 1rem;
}

.ls-guardrails li {
  color: var(--ls-muted);
  font-size: 0.82rem;
  line-height: 1.72;
}

.ls-guardrails li strong {
  color: var(--ls-heading);
  font-weight: 620;
}

.ls-guardrails a {
  color: var(--ls-accent);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.7rem;
  overflow-wrap: anywhere;
}

.ls-guardrails a:hover {
  text-decoration: underline;
  text-underline-offset: 0.2rem;
}

.ls-source-note {
  padding: 1.25rem 2rem 2rem;
  color: var(--ls-muted);
  font-size: 0.75rem;
  line-height: 1.7;
}

/* EXPLAIN */

.explain-tree {
  position: relative;
  display: grid;
  min-height: 31rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  grid-template-rows: repeat(3, auto);
  gap: 2.6rem 7rem;
  margin-top: 1rem;
  padding: 2.5rem clamp(1rem, 5vw, 5rem);
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background:
    linear-gradient(rgba(120, 183, 255, 0.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(120, 183, 255, 0.025) 1px, transparent 1px),
    rgba(7, 12, 20, 0.66);
  background-size: 2rem 2rem;
}

.explain-node {
  position: relative;
  z-index: 2;
  display: flex;
  min-height: 5rem;
  flex-direction: column;
  align-items: flex-start;
  justify-content: center;
  padding: 0.85rem 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  color: var(--ls-copy);
  background: rgba(16, 24, 36, 0.96);
  text-align: left;
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.14);
  cursor: pointer;
  transition:
    border-color 200ms ease,
    box-shadow 200ms ease,
    transform 200ms ease;
}

.explain-node span {
  color: var(--ls-heading);
  font-size: 0.84rem;
  font-weight: 650;
}

.explain-node strong {
  margin-top: 0.35rem;
  color: var(--ls-muted);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.72rem;
  font-weight: 600;
}

.explain-node[data-selected="true"] {
  border-color: rgba(var(--ls-accent-rgb), 0.65);
  box-shadow:
    0 0 0 1px rgba(var(--ls-accent-rgb), 0.16),
    0 18px 45px rgba(var(--ls-accent-rgb), 0.08);
  transform: translateY(-2px);
}

.explain-node--root {
  grid-column: 1 / 3;
  grid-row: 1;
  width: min(18rem, 70%);
  justify-self: center;
}

.explain-node--join {
  grid-column: 1 / 3;
  grid-row: 2;
  width: min(22rem, 75%);
  justify-self: center;
}

.explain-node--left {
  grid-column: 1;
  grid-row: 3;
}

.explain-node--right {
  grid-column: 2;
  grid-row: 3;
}

.explain-tree-lines {
  pointer-events: none;
  position: absolute;
  inset: 0;
}

.explain-tree-lines i {
  position: absolute;
  width: 1px;
  background: rgba(148, 163, 184, 0.25);
}

.explain-tree-lines i:nth-child(1) {
  top: 7.5rem;
  left: 50%;
  height: 4rem;
}

.explain-tree-lines i:nth-child(2),
.explain-tree-lines i:nth-child(3) {
  top: 18rem;
  width: 24%;
  height: 5rem;
  border-top: 1px solid rgba(148, 163, 184, 0.25);
  background: transparent;
}

.explain-tree-lines i:nth-child(2) {
  left: 26%;
  border-left: 1px solid rgba(148, 163, 184, 0.25);
}

.explain-tree-lines i:nth-child(3) {
  right: 26%;
  border-right: 1px solid rgba(148, 163, 184, 0.25);
}

.explain-flow {
  position: absolute;
  z-index: 3;
  width: 0.48rem;
  height: 0.48rem;
  border-radius: 50%;
  background: var(--ls-accent);
  box-shadow: 0 0 14px rgba(var(--ls-accent-rgb), 0.8);
  opacity: 0;
}

.explain-tree[data-step="1"] .explain-flow--right,
.explain-tree[data-step="2"] .explain-flow--left,
.explain-tree[data-step="3"] .explain-flow--root {
  opacity: 1;
  animation: ls-pulse 1.25s ease-in-out infinite;
}

.explain-flow--right {
  right: 26%;
  bottom: 10rem;
}

.explain-flow--left {
  bottom: 14rem;
  left: 50%;
}

.explain-flow--root {
  top: 9rem;
  left: 50%;
}

@keyframes ls-pulse {
  0%,
  100% {
    opacity: 0.35;
    transform: scale(0.75);
  }
  50% {
    opacity: 1;
    transform: scale(1.25);
  }
}

.explain-signal-stage {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(0, 0.85fr);
  gap: 1rem;
  margin-top: 1rem;
}

.explain-plan-line,
.explain-math {
  min-width: 0;
  padding: 1.25rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.25rem;
  background: rgba(10, 16, 25, 0.72);
}

.explain-plan-line > span {
  display: block;
  color: var(--ls-heading);
  font-size: 0.82rem;
  font-weight: 650;
}

.explain-plan-line code {
  display: block;
  margin-top: 1rem;
  padding: 0.8rem;
  overflow-wrap: anywhere;
  color: var(--ls-code);
  background: rgba(var(--ls-accent-rgb), 0.07);
  font-size: 0.78rem;
  line-height: 1.6;
}

.explain-math > p:first-child {
  color: var(--ls-accent);
  font-size: 0.7rem;
  font-weight: 750;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.explain-math > div {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 0.65rem;
  margin-top: 1rem;
}

.explain-math > div span {
  color: var(--ls-muted);
  font-size: 0.72rem;
}

.explain-math > div strong {
  display: block;
  margin-top: 0.2rem;
  color: var(--ls-heading);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 1.25rem;
}

.explain-math > div b {
  color: var(--ls-muted);
  font-size: 0.7rem;
  font-weight: 600;
}

.explain-math h4 {
  margin-top: 1.2rem;
  color: var(--ls-heading);
  font-size: 0.95rem;
}

.explain-math > p:last-child {
  margin-top: 0.45rem;
  color: var(--ls-copy);
  font-size: 0.82rem;
  line-height: 1.68;
}

/* B-tree */

.btree-map {
  position: relative;
  display: grid;
  min-height: 31rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  grid-template-rows: auto auto auto;
  gap: 2.5rem 1rem;
  margin-top: 1rem;
  padding: 2.25rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(6, 13, 19, 0.67);
}

.btree-page {
  position: relative;
  z-index: 2;
  min-height: 5rem;
  padding: 0.85rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  color: var(--ls-copy);
  background: rgba(15, 27, 32, 0.94);
  text-align: left;
  cursor: pointer;
  transition:
    border-color 180ms ease,
    transform 180ms ease,
    box-shadow 180ms ease;
}

.btree-page > span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.btree-page > strong {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.65rem;
}

.btree-page i {
  min-width: 2rem;
  padding: 0.32rem 0.45rem;
  border: 1px solid rgba(148, 163, 184, 0.15);
  border-radius: 0.45rem;
  color: var(--ls-heading);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.76rem;
  font-style: normal;
  text-align: center;
}

.btree-page i[data-key="true"] {
  color: var(--ls-on-accent);
  background: var(--ls-accent);
}

.btree-page[data-selected="true"] {
  border-color: rgba(var(--ls-accent-rgb), 0.65);
  box-shadow: 0 16px 40px rgba(var(--ls-accent-rgb), 0.08);
  transform: translateY(-2px);
}

.btree-page[data-interactive="false"] {
  cursor: default;
}

.btree-page--root {
  grid-column: 1 / 4;
  width: min(18rem, 70%);
  justify-self: center;
}

.btree-page--internal {
  grid-column: 1 / 4;
  width: min(22rem, 78%);
  justify-self: center;
}

.btree-leaves {
  display: grid;
  grid-column: 1 / 4;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.btree-downlink {
  position: absolute;
  z-index: 1;
  left: 50%;
  width: 1px;
  background: rgba(148, 163, 184, 0.25);
}

.btree-downlink--one {
  top: 7.2rem;
  height: 4rem;
}

.btree-downlink--two {
  top: 17.2rem;
  height: 4rem;
}

.btree-range-link {
  position: absolute;
  right: 16%;
  bottom: 1rem;
  color: var(--ls-accent);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.7rem;
  font-weight: 650;
}

.btree-range-link::before {
  content: "";
  position: absolute;
  right: 100%;
  bottom: 0.35rem;
  width: 8rem;
  height: 1px;
  margin-right: 0.5rem;
  background: linear-gradient(90deg, transparent, var(--ls-accent));
}

.btree-split-scene {
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(6, 13, 19, 0.68);
}

.btree-stale-parent {
  width: min(20rem, 70%);
  margin: 0 auto 2rem;
  padding: 0.75rem 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 0.8rem;
  text-align: center;
}

.btree-stale-parent span,
.btree-split-page header span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.btree-stale-parent strong {
  display: block;
  margin-top: 0.2rem;
  color: var(--ls-heading);
  font-size: 0.84rem;
}

.btree-split-pages {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 7rem minmax(0, 1fr);
  align-items: center;
  gap: 1rem;
}

.btree-split-page {
  min-height: 9rem;
  padding: 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(15, 27, 32, 0.94);
  transition:
    opacity 300ms ease,
    transform 350ms ease;
}

.btree-split-page--right[data-visible="false"] {
  opacity: 0.25;
  transform: scale(0.94);
}

.btree-split-page header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

.btree-split-page header strong {
  color: var(--ls-accent);
  font-size: 0.68rem;
}

.btree-split-page > div {
  display: flex;
  gap: 0.55rem;
  margin-top: 1.4rem;
}

.btree-split-page > div span {
  display: grid;
  min-width: 2.4rem;
  height: 2.4rem;
  place-items: center;
  border: 1px solid var(--ls-border);
  border-radius: 0.55rem;
  color: var(--ls-heading);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.76rem;
}

.btree-split-page > div span[data-key="true"] {
  color: var(--ls-on-accent);
  background: var(--ls-accent);
}

.btree-right-link {
  color: var(--ls-accent);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.7rem;
  font-weight: 650;
  text-align: center;
  opacity: 0;
  transition: opacity 250ms ease;
}

.btree-right-link[data-visible="true"] {
  opacity: 1;
}

.btree-right-link i {
  position: relative;
  display: block;
  height: 1px;
  margin-top: 0.45rem;
  background: var(--ls-accent);
}

.btree-right-link i::after {
  content: "";
  position: absolute;
  right: 0;
  bottom: -3px;
  width: 7px;
  height: 7px;
  border-top: 1px solid var(--ls-accent);
  border-right: 1px solid var(--ls-accent);
  transform: rotate(45deg);
}

.btree-search-token {
  margin: 1.5rem auto 0;
  padding: 0.75rem 1rem;
  border: 1px solid rgba(var(--ls-accent-rgb), 0.3);
  border-radius: 999px;
  color: var(--ls-heading);
  background: rgba(var(--ls-accent-rgb), 0.08);
  font-size: 0.72rem;
  text-align: center;
  opacity: 0;
}

.btree-search-token[data-visible="true"] {
  opacity: 1;
}

.btree-search-token span {
  margin-left: 0.6rem;
  color: var(--ls-muted);
}

.btree-ios-chapter .ls-segmented,
.vacuum-horizon-chapter .ls-segmented {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.btree-ios-scene {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 9rem minmax(0, 1fr);
  align-items: center;
  gap: 1rem;
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(6, 13, 19, 0.68);
}

.btree-ios-scene article {
  padding: 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(15, 27, 32, 0.94);
}

.btree-ios-scene article > span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.btree-ios-scene article > strong,
.btree-ios-scene article > code {
  display: block;
  margin-top: 0.55rem;
}

.btree-ios-scene article > strong {
  color: var(--ls-heading);
  font-size: 0.84rem;
}

.btree-ios-scene article > code {
  color: var(--ls-accent);
  background: transparent;
  font-size: 0.76rem;
}

.btree-ios-path {
  color: var(--ls-muted);
  font-size: 0.7rem;
  font-weight: 650;
  text-align: center;
}

.btree-ios-path i {
  position: relative;
  display: block;
  height: 1px;
  margin-bottom: 0.5rem;
  background: var(--ls-accent);
}

.btree-ios-scene > p {
  grid-column: 1 / 4;
  max-width: 43rem;
  margin: 0.5rem auto 0;
  color: var(--ls-copy);
  font-size: 0.84rem;
  line-height: 1.68;
  text-align: center;
}

/* Autovacuum */

.vacuum-trigger-stage {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  gap: 1rem;
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 13, 9, 0.64);
}

.vacuum-gauge,
.vacuum-formula {
  padding: 1.25rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 20, 13, 0.78);
}

.vacuum-gauge {
  display: grid;
  grid-template-columns: auto minmax(5rem, 1fr) auto;
  align-items: center;
  gap: 1rem;
}

.vacuum-gauge > div span {
  display: block;
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.vacuum-gauge > div strong {
  display: block;
  margin-top: 0.3rem;
  color: var(--ls-heading);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 1.05rem;
}

.vacuum-gauge i {
  position: relative;
  height: 0.5rem;
  overflow: hidden;
  border-radius: 999px;
  background: rgba(148, 163, 184, 0.12);
}

.vacuum-gauge i span {
  position: absolute;
  inset: 0;
  width: 82%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--ls-second), var(--ls-accent));
}

.vacuum-formula > span {
  color: var(--ls-accent);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.76rem;
}

.vacuum-formula > strong {
  display: block;
  margin-top: 0.9rem;
  color: var(--ls-heading);
  font-size: 0.92rem;
}

.vacuum-formula p {
  margin-top: 0.45rem;
  color: var(--ls-copy);
  font-size: 0.84rem;
  line-height: 1.68;
}

.vacuum-worker-token {
  grid-column: 1 / 3;
  justify-self: center;
  padding: 0.55rem 0.9rem;
  border: 1px solid rgba(var(--ls-accent-rgb), 0.32);
  border-radius: 999px;
  color: var(--ls-accent-strong);
  background: rgba(var(--ls-accent-rgb), 0.08);
  font-size: 0.74rem;
  font-weight: 700;
}

.vacuum-pass-scene {
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 13, 9, 0.64);
}

.vacuum-pages {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.vacuum-pages article {
  padding: 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 20, 13, 0.78);
}

.vacuum-pages article > span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.vacuum-pages article > div {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.45rem;
  margin-top: 0.8rem;
}

.vacuum-pages i {
  display: grid;
  min-height: 2.35rem;
  place-items: center;
  border: 1px solid var(--ls-border);
  border-radius: 0.45rem;
  color: var(--ls-muted);
  font-size: 0.68rem;
  font-style: normal;
  font-weight: 650;
}

.vacuum-pages i[data-state="dead"] {
  color: var(--ls-danger);
  border-color: color-mix(in srgb, var(--ls-danger) 45%, transparent);
}

.vacuum-pages i[data-state="free"] {
  color: var(--ls-success-soft);
  border-style: dashed;
}

.vacuum-pages i[data-state="frozen"] {
  color: var(--ls-info-soft);
  border-color: color-mix(in srgb, var(--ls-info-soft) 45%, transparent);
}

.vacuum-pass-rail {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.5rem;
  margin-top: 1.25rem;
}

.vacuum-pass-rail span {
  padding: 0.55rem;
  border-radius: 0.5rem;
  color: var(--ls-muted);
  background: rgba(148, 163, 184, 0.06);
  font-size: 0.68rem;
  font-weight: 650;
  text-align: center;
}

.vacuum-pass-rail span[data-active="true"] {
  color: var(--ls-on-accent);
  background: var(--ls-accent);
}

.vacuum-pass-result {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 1.25rem;
  padding: 0.8rem 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 0.75rem;
  color: var(--ls-muted);
  font-size: 0.78rem;
}

.vacuum-pass-result strong {
  color: var(--ls-heading);
}

.vacuum-horizon-scene {
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 13, 9, 0.64);
}

.vacuum-timeline {
  display: grid;
  grid-template-columns: auto minmax(2rem, 1fr) auto minmax(2rem, 1fr) auto;
  align-items: center;
  gap: 0.7rem;
  color: var(--ls-muted);
  font-size: 0.72rem;
}

.vacuum-timeline i {
  height: 1px;
  background: rgba(148, 163, 184, 0.25);
}

.vacuum-timeline strong {
  padding: 0.5rem 0.7rem;
  border-radius: 999px;
  color: var(--ls-accent-strong);
  background: rgba(var(--ls-accent-rgb), 0.09);
  font-size: 0.72rem;
  text-align: center;
}

.vacuum-version-pair {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1.5rem;
}

.vacuum-version-pair article {
  padding: 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 20, 13, 0.78);
}

.vacuum-version-pair article > span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.vacuum-version-pair article > strong,
.vacuum-version-pair article > code {
  display: block;
  margin-top: 0.5rem;
}

.vacuum-version-pair article > strong {
  color: var(--ls-heading);
  font-size: 0.84rem;
}

.vacuum-version-pair article > code {
  color: var(--ls-accent);
  background: transparent;
  font-size: 0.76rem;
}

.vacuum-version-pair article[data-removable="true"] {
  border-color: rgba(105, 208, 173, 0.45);
  box-shadow: 0 14px 35px rgba(105, 208, 173, 0.06);
}

.vacuum-horizon-scene > p {
  max-width: 44rem;
  margin: 1.25rem auto 0;
  color: var(--ls-copy);
  font-size: 0.75rem;
  line-height: 1.7;
  text-align: center;
}

.vacuum-freeze-note {
  max-width: 48rem;
  margin: 1rem auto 0;
  padding: 1.1rem 1.25rem;
  border: 1px solid rgba(120, 183, 255, 0.18);
  border-radius: 1rem;
  background: rgba(120, 183, 255, 0.05);
}

.vacuum-freeze-note > span {
  color: var(--ls-info-soft);
  font-size: 0.68rem;
  font-weight: 750;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.vacuum-freeze-note > strong {
  display: block;
  margin-top: 0.55rem;
  color: var(--ls-heading);
  font-size: 0.88rem;
}

.vacuum-freeze-note p {
  margin-top: 0.45rem;
  color: var(--ls-muted);
  font-size: 0.8rem;
  line-height: 1.68;
}

/* Locks */

.locks-system-picker {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
  margin-top: 2.5rem;
}

.locks-system-picker button {
  min-height: 5rem;
  padding: 0.9rem 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  color: var(--ls-muted);
  background: rgba(17, 14, 23, 0.75);
  text-align: left;
  cursor: pointer;
}

.locks-system-picker button span,
.locks-system-picker button strong {
  display: block;
}

.locks-system-picker button span {
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.locks-system-picker button strong {
  margin-top: 0.35rem;
  color: var(--ls-heading);
  font-size: 0.84rem;
}

.locks-system-picker button[data-selected="true"] {
  border-color: rgba(var(--ls-accent-rgb), 0.55);
  background: rgba(var(--ls-accent-rgb), 0.09);
}

.locks-system-stage {
  display: grid;
  grid-template-columns: minmax(0, 0.75fr) minmax(0, 1.25fr);
  gap: 1rem;
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 10, 18, 0.65);
}

.locks-system-object,
.locks-system-copy {
  padding: 1.25rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 17, 28, 0.78);
}

.locks-system-object {
  display: grid;
  min-height: 12rem;
  place-content: center;
  text-align: center;
}

.locks-system-object span {
  color: var(--ls-muted);
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.locks-system-object strong {
  margin-top: 0.55rem;
  color: var(--ls-heading);
  font-size: 1rem;
}

.locks-system-object i {
  width: 4rem;
  height: 0.3rem;
  margin: 1rem auto 0;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--ls-accent), var(--ls-second));
  box-shadow: 0 0 20px rgba(var(--ls-accent-rgb), 0.35);
}

.locks-system-copy h4 {
  color: var(--ls-heading);
  font-size: 0.95rem;
}

.locks-system-copy > p {
  margin-top: 0.55rem;
  color: var(--ls-copy);
  font-size: 0.84rem;
  line-height: 1.7;
}

.locks-system-copy dl {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.75rem;
  margin-top: 1.2rem;
}

.locks-system-copy dl div {
  padding: 0.75rem;
  border: 1px solid var(--ls-border);
  border-radius: 0.7rem;
}

.locks-system-copy dt {
  color: var(--ls-muted);
  font-size: 0.7rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.locks-system-copy dd {
  margin-top: 0.35rem;
  color: var(--ls-accent-strong);
  font-size: 0.84rem;
}

.locks-queue-scene {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 0.8fr) minmax(0, 1fr);
  gap: 1.5rem 3rem;
  margin-top: 1rem;
  padding: 1.5rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 10, 18, 0.65);
}

.locks-relation,
.locks-holder,
.locks-queue-scene li {
  padding: 1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 17, 28, 0.85);
}

.locks-relation span,
.locks-holder span {
  display: block;
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.locks-relation strong,
.locks-holder strong {
  display: block;
  margin-top: 0.4rem;
  color: var(--ls-heading);
  font-size: 0.86rem;
}

.locks-holder {
  border-color: rgba(105, 208, 173, 0.35);
}

.locks-queue-scene ol {
  display: grid;
  grid-column: 2;
  grid-row: 1 / 3;
  gap: 0.75rem;
}

.locks-queue-scene li {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  opacity: 0.22;
  transition:
    opacity 250ms ease,
    transform 250ms ease;
  transform: translateX(0.5rem);
}

.locks-queue-scene li[data-visible="true"] {
  opacity: 1;
  transform: translateX(0);
}

.locks-queue-scene li > span {
  display: grid;
  width: 1.55rem;
  height: 1.55rem;
  flex: none;
  place-items: center;
  border-radius: 50%;
  color: var(--ls-on-accent);
  background: var(--ls-accent);
  font-size: 0.68rem;
  font-weight: 700;
}

.locks-queue-scene li strong,
.locks-queue-scene li small {
  display: block;
}

.locks-queue-scene li strong {
  color: var(--ls-heading);
  font-size: 0.82rem;
}

.locks-queue-scene li small {
  margin-top: 0.3rem;
  color: var(--ls-muted);
  font-size: 0.74rem;
}

.locks-wait-line {
  position: absolute;
  top: 50%;
  left: 41%;
  width: 8%;
  height: 1px;
  background: linear-gradient(90deg, var(--ls-accent), transparent);
}

.locks-deadlock-scene {
  position: relative;
  display: grid;
  min-height: 24rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  align-items: start;
  gap: 9rem;
  margin-top: 1rem;
  padding: 2rem;
  border: 1px solid var(--ls-border);
  border-radius: 1.5rem;
  background: rgba(15, 10, 18, 0.65);
}

.locks-session {
  position: relative;
  z-index: 2;
  min-height: 9rem;
  padding: 1.1rem;
  border: 1px solid var(--ls-border);
  border-radius: 1rem;
  background: rgba(24, 17, 28, 0.9);
  transition:
    opacity 250ms ease,
    border-color 250ms ease;
}

.locks-session > span {
  color: var(--ls-muted);
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.locks-session > strong,
.locks-session > code {
  display: block;
  margin-top: 0.65rem;
}

.locks-session > strong {
  color: var(--ls-heading);
  font-size: 0.84rem;
}

.locks-session > code {
  color: var(--ls-accent);
  background: transparent;
  font-size: 0.76rem;
}

.locks-session[data-victim="true"] {
  border-color: rgba(255, 151, 140, 0.55);
  opacity: 0.65;
}

.locks-edge {
  position: absolute;
  top: 8rem;
  color: var(--ls-accent);
  font-size: 0.72rem;
  font-weight: 650;
  opacity: 0;
  transition: opacity 250ms ease;
}

.locks-edge[data-visible="true"] {
  opacity: 1;
}

.locks-edge::after {
  content: "";
  position: absolute;
  top: 1.4rem;
  width: 10rem;
  height: 1px;
  background: var(--ls-accent);
}

.locks-edge--a {
  left: 30%;
}

.locks-edge--a::after {
  left: 0;
}

.locks-edge--b {
  right: 30%;
  top: 11rem;
}

.locks-edge--b::after {
  right: 0;
}

.locks-detector {
  position: absolute;
  right: 2rem;
  bottom: 2rem;
  left: 2rem;
  padding: 1rem;
  border: 1px solid rgba(var(--ls-accent-rgb), 0.35);
  border-radius: 1rem;
  background: rgba(var(--ls-accent-rgb), 0.07);
  text-align: center;
  opacity: 0;
  transform: translateY(0.5rem);
  transition:
    opacity 250ms ease,
    transform 250ms ease;
}

.locks-detector[data-visible="true"] {
  opacity: 1;
  transform: translateY(0);
}

.locks-detector span {
  color: var(--ls-muted);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.locks-detector strong {
  display: block;
  margin-top: 0.35rem;
  color: var(--ls-heading);
  font-size: 0.9rem;
}

.locks-detector p {
  margin-top: 0.35rem;
  color: var(--ls-copy);
  font-size: 0.82rem;
  line-height: 1.6;
}

/* Light theme — match MVCC legibility: deeper neutrals, solid surfaces,
   readable code/proof labels, no pale-on-white diagram text. */

[data-theme="light"] .lesson-story {
  --ls-bg: #f3f7fb;
  --ls-surface: rgba(255, 255, 255, 0.9);
  --ls-surface-solid: #ffffff;
  --ls-border: rgba(31, 41, 55, 0.16);
  --ls-copy: #334155;
  --ls-muted: #475569;
  --ls-heading: #0f172a;
  --ls-accent: #0369a1;
  --ls-accent-strong: #0c4a6e;
  --ls-accent-rgb: 3, 105, 161;
  --ls-second: #047857;
  --ls-code: #0c4a6e;
  --ls-code-output: #14532d;
  --ls-on-accent: #ffffff;
  --ls-danger: #be123c;
  --ls-success-soft: #047857;
  --ls-info-soft: #1d4ed8;
  background:
    radial-gradient(circle at 50% 0%, rgba(var(--ls-accent-rgb), 0.1), transparent 34rem),
    linear-gradient(180deg, #f8fafc, #edf3f8);
  box-shadow: 0 28px 75px rgba(23, 42, 65, 0.12);
}

[data-theme="light"] .lesson-story--btree {
  --ls-accent: #047857;
  --ls-accent-strong: #065f46;
  --ls-accent-rgb: 4, 120, 87;
  --ls-second: #1d4ed8;
}

[data-theme="light"] .lesson-story--vacuum {
  --ls-accent: #92400e;
  --ls-accent-strong: #78350f;
  --ls-accent-rgb: 146, 64, 14;
  --ls-second: #047857;
}

[data-theme="light"] .lesson-story--locks {
  --ls-accent: #be123c;
  --ls-accent-strong: #9f1239;
  --ls-accent-rgb: 190, 18, 60;
  --ls-second: #4338ca;
}

[data-theme="light"] .ls-eyebrow,
[data-theme="light"] .ls-chapter-number,
[data-theme="light"] .ls-live-copy > p,
[data-theme="light"] .ls-guardrails > p,
[data-theme="light"] .explain-math > p:first-child,
[data-theme="light"] .vacuum-freeze-note > span {
  color: var(--ls-accent);
}

[data-theme="light"] .ls-memory,
[data-theme="light"] .ls-live-copy > div,
[data-theme="light"] .ls-proof-payoff,
[data-theme="light"] .explain-math > p:last-child,
[data-theme="light"] .locks-system-copy > p {
  color: var(--ls-copy);
}

[data-theme="light"] .ls-play {
  color: var(--ls-accent-strong);
  border-color: rgba(var(--ls-accent-rgb), 0.34);
  background: rgba(var(--ls-accent-rgb), 0.1);
}

[data-theme="light"] .ls-play:hover {
  border-color: rgba(var(--ls-accent-rgb), 0.55);
  background: rgba(var(--ls-accent-rgb), 0.16);
}

[data-theme="light"] .lesson-story button:focus-visible,
[data-theme="light"] .lesson-story summary:focus-visible,
[data-theme="light"] .lesson-story a:focus-visible {
  outline-color: var(--ls-accent);
}

[data-theme="light"] .ls-step-controls,
[data-theme="light"] .ls-segmented,
[data-theme="light"] .ls-proof-disclosure,
[data-theme="light"] .ls-disclosure,
[data-theme="light"] .explain-tree,
[data-theme="light"] .btree-map,
[data-theme="light"] .btree-split-scene,
[data-theme="light"] .btree-ios-scene,
[data-theme="light"] .vacuum-trigger-stage,
[data-theme="light"] .vacuum-pass-scene,
[data-theme="light"] .vacuum-horizon-scene,
[data-theme="light"] .locks-system-stage,
[data-theme="light"] .locks-queue-scene,
[data-theme="light"] .locks-deadlock-scene {
  background-color: rgba(255, 255, 255, 0.72);
  box-shadow: inset 0 0 0 1px rgba(15, 23, 42, 0.04);
}

[data-theme="light"] .explain-node,
[data-theme="light"] .explain-plan-line,
[data-theme="light"] .explain-math,
[data-theme="light"] .btree-page,
[data-theme="light"] .btree-split-page,
[data-theme="light"] .btree-ios-scene article,
[data-theme="light"] .vacuum-gauge,
[data-theme="light"] .vacuum-formula,
[data-theme="light"] .vacuum-pages article,
[data-theme="light"] .vacuum-version-pair article,
[data-theme="light"] .locks-system-picker button,
[data-theme="light"] .locks-system-object,
[data-theme="light"] .locks-system-copy,
[data-theme="light"] .locks-relation,
[data-theme="light"] .locks-holder,
[data-theme="light"] .locks-queue-scene li,
[data-theme="light"] .locks-session,
[data-theme="light"] .ls-call-node,
[data-theme="light"] .ls-guardrails,
[data-theme="light"] .ls-proof-pane,
[data-theme="light"] .ls-call-path {
  background: rgba(255, 255, 255, 0.96);
  box-shadow: 0 12px 35px rgba(31, 54, 78, 0.08);
}

[data-theme="light"] .ls-proof-heading {
  color: #0f172a;
  background: rgba(248, 250, 252, 0.95);
}

[data-theme="light"] .ls-proof-heading small {
  color: #475569;
}

[data-theme="light"] .explain-plan-line code,
[data-theme="light"] .ls-proof-pane pre {
  color: var(--ls-code);
  background: #f8fafc;
  box-shadow: inset 0 0 0 1px rgba(15, 23, 42, 0.06);
}

[data-theme="light"] .ls-proof-output pre {
  color: var(--ls-code-output);
}

[data-theme="light"] .ls-step-controls button[data-selected="true"] {
  color: var(--ls-heading);
  background: rgba(var(--ls-accent-rgb), 0.12);
}

[data-theme="light"] .explain-node[data-selected="true"],
[data-theme="light"] .btree-page[data-selected="true"],
[data-theme="light"] .locks-system-picker button[data-selected="true"] {
  border-color: rgba(var(--ls-accent-rgb), 0.5);
  box-shadow:
    0 0 0 1px rgba(var(--ls-accent-rgb), 0.14),
    0 18px 45px rgba(var(--ls-accent-rgb), 0.12);
}

[data-theme="light"] .vacuum-pages i[data-state="dead"] {
  color: #9f1239;
  background: rgba(190, 18, 60, 0.08);
  border-color: rgba(190, 18, 60, 0.28);
}

[data-theme="light"] .vacuum-pages i[data-state="free"] {
  color: #047857;
  background: rgba(4, 120, 87, 0.07);
  border-color: rgba(4, 120, 87, 0.28);
}

[data-theme="light"] .vacuum-pages i[data-state="frozen"] {
  color: #1d4ed8;
  background: rgba(29, 78, 216, 0.07);
  border-color: rgba(29, 78, 216, 0.28);
}

[data-theme="light"] .vacuum-freeze-note {
  border-color: rgba(29, 78, 216, 0.22);
  background: rgba(239, 246, 255, 0.85);
}

[data-theme="light"] .explain-node strong,
[data-theme="light"] .btree-page > span,
[data-theme="light"] .vacuum-pages article > span,
[data-theme="light"] .locks-relation span,
[data-theme="light"] .locks-holder span,
[data-theme="light"] .locks-session > span,
[data-theme="light"] .locks-queue-scene li small,
[data-theme="light"] .ls-call-node > span,
[data-theme="light"] .ls-call-node p {
  color: #475569;
}

[data-theme="light"] .ls-proof-payoff strong,
[data-theme="light"] .ls-memory strong {
  color: var(--ls-accent-strong);
}

[data-theme="light"] .btree-page i {
  background: #ffffff;
  border-color: rgba(15, 23, 42, 0.12);
  color: #0f172a;
}

[data-theme="light"] .btree-page i[data-key="true"],
[data-theme="light"] .btree-split-page > div span[data-key="true"] {
  color: #ffffff;
  background: var(--ls-accent);
  border-color: transparent;
}

[data-theme="light"] .ls-copy button,
[data-theme="light"] .ls-proof-heading button {
  color: var(--ls-accent-strong);
  border-color: rgba(var(--ls-accent-rgb), 0.28);
  background: #ffffff;
}

[data-theme="light"] .locks-holder {
  border-color: rgba(4, 120, 87, 0.35);
}

[data-theme="light"] .locks-session[data-victim="true"] {
  border-color: rgba(190, 18, 60, 0.4);
}

/* Responsive */

@media (max-width: 900px) {
  .ls-call-path {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .explain-tree {
    gap-inline: 2rem;
  }

  .btree-split-pages {
    grid-template-columns: minmax(0, 1fr) 4rem minmax(0, 1fr);
  }
}

@media (max-width: 720px) {
  .lesson-story {
    border-radius: 1.5rem;
  }

  .ls-intro {
    padding: 3.25rem 1.25rem 2.8rem;
  }

  .ls-chapter {
    padding: 3.5rem 1rem;
  }

  .ls-story-heading {
    align-items: flex-start;
    flex-direction: column;
    gap: 1rem;
  }

  .ls-live-copy {
    min-height: 0;
  }

  .ls-play {
    min-height: 2.75rem;
  }

  .ls-step-controls {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .ls-step-controls button {
    min-height: 3.75rem;
    border-bottom: 1px solid var(--ls-border);
  }

  .ls-step-controls button:nth-child(2) {
    border-right: 0;
  }

  .ls-step-controls button:nth-last-child(-n + 2) {
    border-bottom: 0;
  }

  .ls-segmented {
    grid-template-columns: 1fr;
  }

  .ls-segmented button {
    min-height: 3.1rem;
  }

  .ls-rule {
    align-items: flex-start;
    flex-direction: column;
    gap: 0.55rem;
  }

  .ls-proof-grid {
    grid-template-columns: 1fr;
  }

  .ls-proof-pane {
    border-right: 0;
    border-bottom: 1px solid var(--ls-border);
  }

  .ls-proof-pane:last-child {
    border-bottom: 0;
  }

  .ls-proof-pane pre {
    max-height: 24rem;
    font-size: 0.71rem;
  }

  .ls-source-trail summary {
    padding-inline: 1.25rem;
  }

  .ls-call-path {
    grid-template-columns: 1fr;
    margin-inline: 1rem;
  }

  .ls-guardrails {
    margin-inline: 1rem;
  }

  .ls-guardrails ul {
    grid-template-columns: 1fr;
  }

  .ls-guardrails a {
    display: inline-flex;
    min-height: 2.75rem;
    align-items: center;
  }

  .ls-source-note {
    padding-inline: 1.25rem;
  }

  .explain-tree {
    min-height: 35rem;
    grid-template-columns: 1fr;
    grid-template-rows: repeat(4, auto);
    gap: 1rem;
    padding: 1.25rem;
  }

  .explain-node--root,
  .explain-node--join,
  .explain-node--left,
  .explain-node--right {
    width: 100%;
    grid-column: 1;
    justify-self: stretch;
  }

  .explain-node--root {
    grid-row: 4;
  }

  .explain-node--join {
    grid-row: 3;
  }

  .explain-node--left {
    grid-row: 1;
  }

  .explain-node--right {
    grid-row: 2;
  }

  .explain-tree-lines,
  .explain-flow {
    display: none;
  }

  .explain-signal-stage {
    grid-template-columns: 1fr;
  }

  .btree-map {
    min-height: auto;
    padding: 1.25rem;
  }

  .btree-page--root,
  .btree-page--internal {
    width: 100%;
  }

  .btree-leaves {
    grid-template-columns: 1fr;
  }

  .btree-downlink,
  .btree-range-link {
    display: none;
  }

  .btree-split-pages {
    grid-template-columns: 1fr;
  }

  .btree-right-link {
    width: 1px;
    height: 3rem;
    justify-self: center;
  }

  .btree-right-link i {
    width: 1px;
    height: 100%;
    margin: 0 auto;
  }

  .btree-right-link i::after {
    top: auto;
    right: -3px;
    bottom: 0;
    transform: rotate(135deg);
  }

  .btree-search-token span {
    display: block;
    margin: 0.35rem 0 0;
  }

  .btree-ios-chapter .ls-segmented,
  .vacuum-horizon-chapter .ls-segmented {
    grid-template-columns: 1fr;
  }

  .btree-ios-scene {
    grid-template-columns: 1fr;
  }

  .btree-ios-scene > p {
    grid-column: 1;
  }

  .btree-ios-path i {
    width: 1px;
    height: 2rem;
    margin: 0 auto 0.5rem;
  }

  .vacuum-trigger-stage,
  .vacuum-version-pair,
  .locks-system-stage {
    grid-template-columns: 1fr;
  }

  .vacuum-worker-token {
    grid-column: 1;
  }

  .vacuum-gauge {
    grid-template-columns: 1fr;
  }

  .vacuum-pages {
    grid-template-columns: 1fr;
  }

  .vacuum-pass-rail {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .vacuum-pass-result {
    align-items: flex-start;
    flex-direction: column;
  }

  .vacuum-timeline {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .vacuum-timeline i {
    width: 1px;
    height: 1.2rem;
    margin: auto;
  }

  .locks-system-picker {
    grid-template-columns: 1fr;
  }

  .locks-system-picker button {
    min-height: 4.5rem;
  }

  .locks-queue-scene {
    grid-template-columns: 1fr;
    gap: 0.75rem;
  }

  .locks-queue-scene ol {
    grid-column: 1;
    grid-row: auto;
  }

  .locks-wait-line {
    display: none;
  }

  .locks-deadlock-scene {
    min-height: 35rem;
    grid-template-columns: 1fr;
    gap: 1rem;
  }

  .locks-edge {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .lesson-story *,
  .lesson-story *::before,
  .lesson-story *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}