.energy-chapter { margin-top:96px; }
.energy-index {
  background:linear-gradient(145deg,color-mix(in srgb,var(--accent-3) 8%,var(--panel)),var(--panel));
}
.energy-index::after { border-color:color-mix(in srgb,var(--accent-3) 28%,transparent); }

.energy-definition-grid {
  display:grid;
  grid-template-columns:repeat(3,minmax(0,1fr));
  gap:12px;
}
.energy-definition-grid article {
  min-width:0;
  padding:26px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.energy-icon {
  display:grid;
  place-items:center;
  width:42px;
  height:42px;
  border:1px solid var(--line-strong);
  border-radius:12px;
  color:var(--accent-3);
  font-family:"Cambria Math","STIX Two Math",Georgia,serif;
  font-size:1.2rem;
  font-weight:800;
}
.energy-definition-grid h3 { margin:16px 0 8px; }
.energy-definition-grid p { margin:10px 0 0; color:var(--muted); font-size:.86rem; }
.energy-total-card {
  background:linear-gradient(145deg,color-mix(in srgb,var(--accent) 5%,var(--panel)),var(--panel)) !important;
}

.energy-derivation {
  display:grid;
  grid-template-columns:minmax(0,1fr) auto minmax(0,1fr) auto minmax(0,1.15fr);
  gap:12px;
  align-items:stretch;
}
.energy-derivation article {
  padding:24px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.energy-derivation h3 { margin:14px 0 8px; font-size:1rem; }
.derivation-arrow {
  display:grid;
  place-items:center;
  color:var(--accent);
  font-size:1.45rem;
}
.conservation-note {
  display:flex;
  gap:16px;
  align-items:flex-start;
  margin-top:12px;
  padding:18px 20px;
  border-left:3px solid var(--accent-3);
  background:color-mix(in srgb,var(--accent-3) 5%,transparent);
}
.conservation-note strong { white-space:nowrap; }
.conservation-note p { margin:0; color:var(--muted); }

.energy-lab-section {
  background:
    radial-gradient(circle at 15% 15%,color-mix(in srgb,var(--accent-3) 7%,transparent),transparent 32%),
    linear-gradient(180deg,color-mix(in srgb,var(--accent) 3%,transparent),transparent 24%);
}
.energy-lab {
  display:grid;
  grid-template-columns:270px minmax(0,1fr);
  gap:12px;
  align-items:start;
}
.energy-controls {
  position:sticky;
  top:calc(var(--header-h) + 16px);
  display:grid;
  gap:22px;
  padding:22px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel-solid);
}
.energy-actions { display:grid; grid-template-columns:1fr 1fr; gap:8px; }
.energy-main { min-width:0; display:grid; gap:12px; }

.energy-metrics {
  display:grid;
  grid-template-columns:repeat(4,minmax(0,1fr));
  overflow:hidden;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.energy-metrics article {
  min-width:0;
  padding:15px 16px;
  border-right:1px solid var(--line);
}
.energy-metrics article:last-child { border-right:0; }
.energy-metrics span { display:block; color:var(--muted); font-size:.66rem; font-weight:740; }
.energy-metrics strong { display:inline-block; margin-top:5px; font-size:1.08rem; font-variant-numeric:tabular-nums; }
.energy-metrics small { margin-left:4px; color:var(--muted); font-size:.6rem; }

.energy-visual-grid {
  display:grid;
  grid-template-columns:minmax(0,1.3fr) minmax(300px,.7fr);
  gap:12px;
}
.energy-mech-stage { min-height:270px; }
.energy-mech-stage svg { width:100%; height:100%; min-height:270px; }
.energy-mass {
  fill:color-mix(in srgb,var(--accent) 18%,var(--panel-solid));
  stroke:var(--accent);
  stroke-width:2;
}
.energy-velocity {
  stroke:var(--accent-2);
  stroke-width:4;
  stroke-linecap:round;
}
.track-line { stroke:var(--line-strong); stroke-width:3; }
.guide-line { stroke:var(--line); stroke-width:1; stroke-dasharray:5 6; }
.eq-dot { fill:var(--muted); }
.eq-text { fill:var(--muted); font-size:11px; }

.energy-state-row {
  display:grid;
  grid-template-columns:repeat(3,1fr);
  border-top:1px solid var(--line);
}
.energy-state-row > div {
  display:grid;
  grid-template-columns:auto 1fr auto;
  gap:6px;
  align-items:baseline;
  padding:13px 15px;
  border-right:1px solid var(--line);
}
.energy-state-row > div:last-child { border-right:0; }
.energy-state-row span { color:var(--accent-2); font-size:.7rem; font-weight:850; }
.energy-state-row strong { justify-self:end; font-variant-numeric:tabular-nums; }
.energy-state-row small { color:var(--muted); font-size:.6rem; }

.energy-percent {
  color:var(--accent-3);
  font-size:.72rem;
  font-weight:800;
}
.energy-bars { display:grid; gap:20px; padding:22px 20px; }
.energy-bar-label {
  display:flex;
  justify-content:space-between;
  gap:12px;
  align-items:baseline;
  margin-bottom:8px;
}
.energy-bar-label span { color:var(--muted); font-size:.74rem; }
.energy-bar-label strong { font-size:.8rem; font-variant-numeric:tabular-nums; }
.energy-bar-track {
  height:18px;
  overflow:hidden;
  border-radius:999px;
  background:color-mix(in srgb,var(--line-strong) 65%,transparent);
}
.energy-bar {
  display:block;
  height:100%;
  width:0;
  border-radius:inherit;
}
.energy-bar.potential { background:var(--accent-3); }
.energy-bar.kinetic { background:var(--accent-2); }
.energy-balance {
  display:grid;
  grid-template-columns:auto 1fr auto;
  align-items:center;
  gap:10px;
  padding:0 20px 18px;
}
.energy-balance > span { color:var(--muted); font-size:.68rem; }
.balance-track {
  display:flex;
  overflow:hidden;
  height:12px;
  border-radius:999px;
  background:var(--line);
}
.balance-potential,
.balance-kinetic { display:block; height:100%; }
.balance-potential { background:var(--accent-3); }
.balance-kinetic { background:var(--accent-2); }
.energy-storage > p { margin:0; padding:0 20px 20px; color:var(--muted); font-size:.75rem; }

.energy-plot { margin:0; }
.energy-plot figcaption {
  display:block;
  padding:18px 20px;
  border-bottom:1px solid var(--line);
}
.energy-plot figcaption span {
  display:block;
  color:var(--muted);
  font-size:.68rem;
  font-weight:750;
  letter-spacing:.06em;
  text-transform:uppercase;
}
.energy-plot figcaption strong { display:block; margin-top:3px; font-size:.92rem; }
.energy-plot svg { width:100%; min-height:315px; }
.energy-trace {
  fill:none;
  vector-effect:non-scaling-stroke;
  stroke-linecap:round;
  stroke-linejoin:round;
}
.energy-trace.total { stroke:var(--text); stroke-width:2.2; stroke-dasharray:8 6; opacity:.78; }
.energy-trace.potential { stroke:var(--accent-3); stroke-width:3; }
.energy-trace.kinetic { stroke:var(--accent-2); stroke-width:3; }
.energy-time-line { stroke:var(--line-strong); stroke-width:1; stroke-dasharray:4 5; }
.energy-marker {
  stroke:var(--bg);
  stroke-width:2;
}
.energy-marker.potential { fill:var(--accent-3); }
.energy-marker.kinetic { fill:var(--accent-2); }
.energy-legend {
  display:flex;
  flex-wrap:wrap;
  gap:18px;
  padding:0 20px 18px;
  color:var(--muted);
  font-size:.7rem;
}
.energy-legend span { display:flex; align-items:center; gap:7px; }
.energy-legend i { width:20px; height:3px; display:inline-block; border-radius:999px; }
.legend-total { background:var(--text); }
.legend-potential { background:var(--accent-3); }
.legend-kinetic { background:var(--accent-2); }

.double-frequency-grid {
  display:grid;
  grid-template-columns:repeat(3,minmax(0,1fr));
  gap:12px;
}
.double-frequency-grid article {
  padding:24px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.double-frequency-result {
  display:grid;
  align-content:center;
}
.double-frequency-result strong {
  color:var(--accent);
  font-family:"Cambria Math","STIX Two Math",Georgia,serif;
  font-size:3.8rem;
  line-height:1;
}
.double-frequency-result p { margin:10px 0 0; color:var(--muted); }

.storage-network {
  display:grid;
  grid-template-columns:minmax(0,1fr) auto minmax(0,1fr);
  align-items:stretch;
  gap:16px;
}
.storage-network article {
  padding:26px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.storage-network article > span {
  color:var(--accent);
  font-size:.72rem;
  font-weight:850;
  letter-spacing:.06em;
  text-transform:uppercase;
}
.storage-network strong { display:block; margin:9px 0 6px; }
.storage-network p { margin:0; color:var(--muted); }
.storage-flow {
  display:grid;
  place-items:center;
  align-content:center;
  color:var(--accent-3);
}
.storage-flow span { font-size:2.2rem; }
.storage-flow small { color:var(--muted); text-align:center; }
.storage-network-note {
  max-width:820px;
  margin:18px 0 0;
  color:var(--muted);
}

@media (max-width:1080px) {
  .energy-visual-grid { grid-template-columns:1fr; }
  .energy-storage { display:grid; grid-template-columns:1fr 1fr; }
  .energy-storage .panel-head { grid-column:1/-1; }
  .energy-storage > p { align-self:center; }
}
@media (max-width:980px) {
  .energy-definition-grid { grid-template-columns:1fr 1fr; }
  .energy-total-card { grid-column:1/-1; }
  .energy-derivation { grid-template-columns:1fr; }
  .derivation-arrow { transform:rotate(90deg); min-height:22px; }
  .energy-lab { grid-template-columns:1fr; }
  .energy-controls { position:static; grid-template-columns:1fr 1fr; }
  .energy-actions { align-self:end; }
  .double-frequency-grid { grid-template-columns:1fr 1fr; }
  .double-frequency-result { grid-column:1/-1; }
}
@media (max-width:720px) {
  .energy-chapter { margin-top:58px; }
  .energy-definition-grid,
  .double-frequency-grid,
  .storage-network { grid-template-columns:1fr; }
  .energy-total-card,
  .double-frequency-result { grid-column:auto; }
  .storage-flow span { transform:rotate(90deg); }
  .energy-controls { grid-template-columns:1fr; }
  .energy-metrics { grid-template-columns:1fr 1fr; }
  .energy-metrics article:nth-child(2) { border-right:0; }
  .energy-metrics article:nth-child(-n+2) { border-bottom:1px solid var(--line); }
  .energy-storage { display:block; }
  .energy-state-row { grid-template-columns:1fr; }
  .energy-state-row > div { border-right:0; border-bottom:1px solid var(--line); }
  .energy-state-row > div:last-child { border-bottom:0; }
  .energy-plot svg { min-height:255px; }
  .conservation-note { display:block; }
  .conservation-note p { margin-top:8px; }
}