.coupled-chapter { margin-top:96px; }
.coupled-index {
  background:linear-gradient(145deg,color-mix(in srgb,var(--accent-2) 8%,var(--panel)),var(--panel));
}
.coupled-index::after { border-color:color-mix(in srgb,var(--accent-2) 30%,transparent); }

.coupled-model-grid,
.mode-grid,
.coupled-energy-grid,
.coupled-bridge-grid {
  display:grid;
  grid-template-columns:repeat(3,minmax(0,1fr));
  gap:12px;
}
.coupled-model-grid article,
.mode-grid article,
.coupled-energy-grid article,
.coupled-bridge-grid article {
  min-width:0;
  padding:24px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.coupled-model-grid h3,
.mode-grid h3 { margin:14px 0 8px; }
.coupled-model-grid p,
.mode-grid p,
.coupled-energy-grid p,
.coupled-bridge-grid p {
  margin:9px 0 0;
  color:var(--muted);
  font-size:.84rem;
}
.coupled-primary {
  background:linear-gradient(145deg,color-mix(in srgb,var(--accent) 7%,var(--panel)),var(--panel)) !important;
}
.coupled-modal {
  background:linear-gradient(145deg,color-mix(in srgb,var(--accent-3) 7%,var(--panel)),var(--panel)) !important;
}
.coupled-equation {
  min-height:96px;
  overflow-x:auto;
  justify-content:flex-start;
  font-size:clamp(.92rem,1.4vw,1.12rem);
}
.matrix-equation {
  display:grid;
  gap:8px;
  justify-items:start;
  white-space:nowrap;
}
.mode-grid { grid-template-columns:1fr 1fr; }
.mode-card { position:relative; overflow:hidden; }
.mode-card::after {
  content:"";
  position:absolute;
  width:150px;
  height:150px;
  right:-80px;
  top:-82px;
  border:1px solid color-mix(in srgb,var(--accent) 22%,transparent);
  border-radius:50%;
}
.mode-card.anti::after { border-color:color-mix(in srgb,var(--accent-2) 28%,transparent); }
.mode-shape {
  display:grid;
  grid-template-columns:auto 1fr auto 1fr auto 1fr auto;
  gap:8px;
  align-items:center;
  margin:20px 0 16px;
  color:var(--muted);
}
.mode-wall { width:5px; height:54px; border-left:3px solid var(--muted); opacity:.75; }
.mode-wall.right { border-left:0; border-right:3px solid var(--muted); }
.mode-spring { height:2px; background:var(--line-strong); }
.mode-spring.coupling { background:var(--accent-3); }
.mode-transform-grid { margin-top:12px; }
.mode-mass {
  width:44px;
  height:44px;
  display:grid;
  place-items:center;
  border-radius:11px;
  background:color-mix(in srgb,var(--accent) 70%,var(--accent-2));
  color:#07131c;
  font-size:.72rem;
  font-weight:900;
}
.mode-card.anti .mode-mass { background:color-mix(in srgb,var(--accent-2) 74%,var(--accent)); }
.mode-arrows { display:flex; justify-content:center; gap:50px; margin-top:8px; font-size:1.45rem; }
.mode-arrows .a1,.mode-arrows .a2 { color:var(--accent); }
.mode-card.anti .mode-arrows .a2 { color:var(--accent-2); transform:rotate(180deg); }
.mode-card.anti .mode-arrows .a1 { color:var(--accent-2); }

.coupled-lab-section {
  background:
    radial-gradient(circle at 10% 20%,color-mix(in srgb,var(--accent-2) 7%,transparent),transparent 30%),
    linear-gradient(180deg,color-mix(in srgb,var(--accent) 3%,transparent),transparent 26%);
}
.coupled-lab {
  display:grid;
  grid-template-columns:280px minmax(0,1fr);
  gap:12px;
  align-items:start;
}
.coupled-controls {
  position:sticky;
  top:calc(var(--header-h) + 16px);
  display:grid;
  gap:19px;
  padding:22px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel-solid);
}
.coupled-presets { display:grid; grid-template-columns:repeat(3,1fr); gap:6px; }
.coupled-presets button {
  min-width:0;
  min-height:36px;
  padding:0 6px;
  border:1px solid var(--line);
  border-radius:9px;
  background:var(--panel);
  color:var(--muted);
  font-size:.65rem;
  font-weight:760;
  cursor:pointer;
}
.coupled-presets button:hover,.coupled-presets button:focus-visible { color:var(--text); border-color:var(--line-strong); }
.coupled-main { min-width:0; display:grid; gap:12px; }
.coupled-metrics {
  display:grid;
  grid-template-columns:repeat(6,minmax(0,1fr));
  overflow:hidden;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--panel);
}
.coupled-metrics article {
  min-width:0;
  padding:14px 12px;
  border-right:1px solid var(--line);
}
.coupled-metrics article:last-child { border-right:0; }
.coupled-metrics span { display:block; color:var(--muted); font-size:.62rem; font-weight:760; }
.coupled-metrics strong {
  display:inline-block;
  margin-top:5px;
  max-width:100%;
  overflow:hidden;
  text-overflow:ellipsis;
  font-size:.94rem;
  font-variant-numeric:tabular-nums;
  white-space:nowrap;
}
.coupled-metrics small { margin-left:4px; color:var(--muted); font-size:.54rem; }

.coupled-mechanics svg {
  width:100%;
  min-height:280px;
  background:linear-gradient(180deg,color-mix(in srgb,var(--bg-elevated) 45%,transparent),transparent);
}
.c-track { stroke:var(--line-strong); stroke-width:3; }
.c-equilibrium { stroke:var(--line); stroke-width:1; stroke-dasharray:5 6; }
.c-wall line { stroke:var(--muted); stroke-width:3; }
.c-spring {
  fill:none;
  stroke:var(--accent);
  stroke-width:3.8;
  stroke-linejoin:round;
  stroke-linecap:round;
  vector-effect:non-scaling-stroke;
}
.c-spring.coupling { stroke:var(--accent-3); }
.c-mass rect { fill:url(#coupledMassGrad); stroke:color-mix(in srgb,var(--text) 18%,transparent); stroke-width:2; }
.c-mass.second rect { fill:url(#coupledMassGrad2); }
.c-mass text { fill:#07131c; font-size:25px; font-weight:900; }
.c-svg-label { fill:var(--muted); font:600 14px system-ui,sans-serif; }
.c-svg-value { fill:var(--text); font:760 14px system-ui,sans-serif; }
.c-coupling-label { fill:var(--accent-3); font:800 13px system-ui,sans-serif; }
.c-direction { stroke:var(--warm); stroke-width:2.4; vector-effect:non-scaling-stroke; }
.c-direction-head { fill:var(--warm); }

.coupled-state-grid {
  display:grid;
  grid-template-columns:repeat(6,minmax(0,1fr));
  border-top:1px solid var(--line);
}
.coupled-state-grid > div {
  display:grid;
  grid-template-columns:auto 1fr auto;
  gap:6px;
  align-items:baseline;
  min-width:0;
  padding:12px 13px;
  border-right:1px solid var(--line);
}
.coupled-state-grid > div:last-child { border-right:0; }
.coupled-state-grid span { color:var(--accent-2); font-size:.65rem; font-weight:850; }
.coupled-state-grid strong { justify-self:end; min-width:0; font-size:.79rem; font-variant-numeric:tabular-nums; }
.coupled-state-grid small { color:var(--muted); font-size:.52rem; }

.coupled-plot-grid { display:grid; grid-template-columns:1fr 1fr; gap:12px; }
.coupled-plot { margin:0; }
.coupled-plot figcaption {
  display:flex;
  justify-content:space-between;
  gap:18px;
  align-items:flex-end;
  padding:18px 20px;
  border-bottom:1px solid var(--line);
}
.coupled-plot figcaption > div > span {
  display:block;
  color:var(--muted);
  font-size:.68rem;
  font-weight:750;
  letter-spacing:.06em;
  text-transform:uppercase;
}
.coupled-plot figcaption strong { display:block; margin-top:3px; font-size:.92rem; }
.coupled-plot figcaption p { margin:0; max-width:245px; color:var(--muted); font-size:.69rem; text-align:right; }
.coupled-plot svg { display:block; width:100%; min-height:265px; }
.c-trace {
  fill:none;
  stroke-width:2.55;
  stroke-linecap:round;
  stroke-linejoin:round;
  vector-effect:non-scaling-stroke;
}
.c-trace.x1,.c-trace.qs { stroke:var(--accent); }
.c-trace.x2,.c-trace.qa { stroke:var(--accent-2); }
.c-marker { stroke:var(--bg); stroke-width:2; vector-effect:non-scaling-stroke; }
.c-marker.x1,.c-marker.qs { fill:var(--accent); }
.c-marker.x2,.c-marker.qa { fill:var(--accent-2); }
.c-time-line { stroke:var(--warm); stroke-width:1.1; stroke-dasharray:4 5; vector-effect:non-scaling-stroke; }
.coupled-legend { display:flex; flex-wrap:wrap; gap:16px; padding:0 18px 16px; color:var(--muted); font-size:.68rem; }
.coupled-legend span { display:flex; align-items:center; gap:7px; }
.coupled-legend i { width:18px; height:2px; display:inline-block; }
.coupled-legend .l1 { background:var(--accent); }
.coupled-legend .l2 { background:var(--accent-2); }
.coupled-interpretation {
  padding:20px 22px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:linear-gradient(110deg,color-mix(in srgb,var(--accent-3) 5%,var(--panel)),var(--panel));
}
.coupled-interpretation > span {
  color:var(--muted);
  font-size:.65rem;
  font-weight:760;
  letter-spacing:.07em;
  text-transform:uppercase;
}
.coupled-interpretation strong { display:block; margin-top:7px; font-size:1.04rem; }
.coupled-interpretation p { margin:7px 0 0; color:var(--muted); font-size:.79rem; }

.coupled-energy-grid article > span,
.coupled-bridge-grid article > span {
  color:var(--accent-2);
  font-size:.67rem;
  font-weight:850;
  letter-spacing:.07em;
  text-transform:uppercase;
}
.coupled-energy-grid strong,
.coupled-bridge-grid strong { display:block; margin-top:8px; font-size:1.02rem; }
.coupled-limit {
  background:linear-gradient(145deg,color-mix(in srgb,var(--warm) 5%,var(--panel)),var(--panel)) !important;
}

@media (max-width:1120px) {
  .coupled-metrics { grid-template-columns:repeat(3,1fr); }
  .coupled-metrics article:nth-child(3n) { border-right:0; }
  .coupled-metrics article:nth-child(-n+3) { border-bottom:1px solid var(--line); }
  .coupled-state-grid { grid-template-columns:repeat(3,1fr); }
  .coupled-state-grid > div:nth-child(3n) { border-right:0; }
  .coupled-state-grid > div:nth-child(-n+3) { border-bottom:1px solid var(--line); }
}
@media (max-width:980px) {
  .coupled-model-grid,.coupled-energy-grid,.coupled-bridge-grid { grid-template-columns:1fr 1fr; }
  .coupled-model-grid > :last-child,.coupled-energy-grid > :last-child,.coupled-bridge-grid > :last-child { grid-column:1/-1; }
  .coupled-lab { grid-template-columns:1fr; }
  .coupled-controls { position:static; grid-template-columns:1fr 1fr; }
  .coupled-controls .lab-actions,.coupled-controls .coupled-presets { align-self:end; }
  .coupled-plot-grid { grid-template-columns:1fr; }
}
@media (max-width:760px) {
  .coupled-chapter { margin-top:58px; }
  .coupled-model-grid,.mode-grid,.coupled-energy-grid,.coupled-bridge-grid,.coupled-controls { grid-template-columns:1fr; }
  .coupled-model-grid > :last-child,.coupled-energy-grid > :last-child,.coupled-bridge-grid > :last-child { grid-column:auto; }
  .coupled-metrics,.coupled-state-grid { grid-template-columns:1fr 1fr; }
  .coupled-metrics article,.coupled-state-grid > div { border-right:1px solid var(--line); border-bottom:1px solid var(--line); }
  .coupled-metrics article:nth-child(2n),.coupled-state-grid > div:nth-child(2n) { border-right:0; }
  .coupled-metrics article:nth-child(3n),.coupled-state-grid > div:nth-child(3n) { border-right:1px solid var(--line); }
  .coupled-metrics article:nth-last-child(-n+2),.coupled-state-grid > div:nth-last-child(-n+2) { border-bottom:0; }
  .coupled-plot figcaption { display:block; }
  .coupled-plot figcaption p { margin-top:7px; text-align:left; }
  .coupled-plot svg { min-height:235px; }
  .coupled-mechanics svg { min-height:245px; }
}
@media (max-width:430px) {
  .coupled-presets { grid-template-columns:1fr; }
  .coupled-metrics,.coupled-state-grid { grid-template-columns:1fr; }
  .coupled-metrics article,.coupled-metrics article:nth-child(2n),.coupled-metrics article:nth-child(3n),
  .coupled-state-grid > div,.coupled-state-grid > div:nth-child(2n),.coupled-state-grid > div:nth-child(3n) { border-right:0; border-bottom:1px solid var(--line); }
  .coupled-metrics article:last-child,.coupled-state-grid > div:last-child { border-bottom:0; }
}
.axis-tick { fill:var(--muted); font:600 11px system-ui,sans-serif; }