/* Lecture 02: exponentials, PoE, and URDF. */
.lecture-02 .slide-kicker {
  margin: 0 0 0.3rem;
  color: var(--epfl-red);
  font-size: var(--font-small);
  font-weight: 800;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.lecture-02 .slide-title {
  margin-bottom: 0.3rem;
  font-size: clamp(2rem, 3vw, 3.45rem);
}

.lecture-02 .slide-subtitle {
  max-width: 82ch;
  margin: 0 0 var(--vgap-sm);
  color: var(--muted);
  font-size: clamp(1rem, 1.3vw, 1.42rem);
  line-height: 1.34;
}

.lecture-02-title { white-space: nowrap; }
.lecture-02 .lecture-promise {
  max-width: 62ch;
  margin: var(--vgap-md) auto 0;
  padding-top: var(--vgap-sm);
  border-top: 1px solid var(--line);
  color: var(--muted);
}

.lecture-02 .definition {
  border-left-color: var(--epfl-red);
  background: #f8f8f8;
}

.lecture-02 .definition p { margin: 0.35rem 0; }
.lecture-02 .clean-callout,
.lecture-02 .slide-takeaway,
.lecture-02 .demo-prompt,
.lecture-02 .bridge-note {
  padding: 0.45rem 0.65rem;
  border-left: 3px solid var(--epfl-red);
  background: color-mix(in srgb, var(--epfl-red) 4%, white);
  line-height: 1.35;
}
.lecture-02 .slide-takeaway,
.lecture-02 .bridge-note { margin-top: var(--vgap-sm); color: var(--muted); }
.lecture-02 .demo-prompt { margin: 0 0 0.5rem; }

.representation-path {
  flex: 1;
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr;
  gap: 0.75rem;
  align-items: center;
}
.representation-node {
  min-height: 12rem;
  padding: 1rem;
  border: 1px solid var(--line);
  border-top: 5px solid var(--black);
  background: var(--white);
}
.representation-node:nth-of-type(2) { border-top-color: var(--epfl-red); }
.representation-node span {
  display: block;
  color: var(--epfl-red);
  font-size: var(--font-h3);
  font-weight: 800;
}
.representation-node strong { display: block; margin-top: 0.5rem; font-size: var(--font-h3); }
.representation-arrow { font-size: var(--font-h3); color: var(--muted); }

.notation-grid {
  flex: 1;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
  min-height: 0;
}
.notation-grid .definition { margin: 0; min-height: 0; }
.notation-grid.compact { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.notation-grid.compact .definition { padding: 0.7rem; }

.skew-card {
  align-self: center;
  padding: 1rem;
  border: 1px solid var(--line);
  border-top: 4px solid var(--black);
}

.rodrigues-series { font-size: clamp(1rem, 1.45vw, 1.55rem); }
.series-card {
  align-self: center;
  padding: 0.65rem;
  border-top: 3px solid var(--black);
  background: #fafafa;
  text-align: center;
}
.series-card:last-child { border-top-color: var(--epfl-red); }
.series-card .equation { margin-block: 0.45rem; }
.rodrigues-meaning {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.55rem;
  margin: var(--vgap-sm) 0;
}
.rodrigues-meaning > div {
  padding: 0.65rem;
  border-top: 4px solid var(--black);
  background: #fafafa;
}
.rodrigues-meaning > div:nth-child(2) { border-top-color: var(--epfl-red); }
.rodrigues-meaning p { margin-bottom: 0; }

.adjoint-layout {
  display: grid;
  grid-template-columns: minmax(18rem, .72fr) minmax(0, 1.28fr);
  gap: 0.7rem;
}
.adjoint-layout .definition { margin: 0; }
.adjoint-formula {
  padding: 0.65rem;
  border: 1px solid var(--line);
  border-top: 4px solid var(--black);
}
.adjoint-formula .equation { margin-block: 0.35rem; }
.adjoint-uses {
  flex: 1;
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.45rem;
  margin-top: 0.6rem;
  min-height: 0;
}
.adjoint-uses > div {
  padding: 0.55rem;
  border-top: 3px solid var(--black);
  background: #fafafa;
}
.adjoint-uses > div:nth-child(2) { border-top-color: var(--epfl-red); }
.adjoint-uses p { margin: 0.3rem 0 0; font-size: 0.9em; }
.screw-cases { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0.55rem; align-content: center; height: 100%; }
.screw-cases > div { padding: 0.8rem; border-top: 4px solid var(--black); background: #fafafa; }
.screw-cases > div:nth-child(2) { border-top-color: var(--epfl-red); }

.lecture-table {
  width: min(76rem, 100%);
  margin: auto;
  border-collapse: collapse;
  font-variant-numeric: tabular-nums;
}
.lecture-table th,
.lecture-table td { padding: 0.62rem; border-bottom: 1px solid var(--line); text-align: center; }
.lecture-table th { border-bottom: 3px solid var(--black); }
.lecture-table tbody tr:nth-child(2) { background: #fafafa; }

.code-card {
  margin: 0;
  padding: 0.75rem;
  overflow: auto;
  border: 1px solid var(--line);
  border-left: 4px solid var(--epfl-red);
  background: #f7f7f7;
  color: #222;
  font: 0.78em/1.35 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  white-space: pre-wrap;
}

.urdf-tree {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.32rem;
  margin: var(--vgap-sm) 0 var(--vgap-md);
}
.urdf-node { padding: 0.55rem 0.7rem; border: 2px solid var(--black); background: var(--white); font-weight: 800; }
.urdf-node.root { border-color: var(--epfl-red); }
.urdf-node.tool { background: var(--black); color: var(--white); }
.urdf-edge { padding: 0.25rem 0.45rem; border-bottom: 2px solid var(--epfl-red); color: var(--muted); font-size: 0.85em; }
.urdf-edge.fixed { border-bottom-style: dashed; }

.urdf-tag-card {
  min-width: 0;
  padding: 0.8rem;
  border: 1px solid var(--line);
  border-top: 4px solid var(--black);
}
.urdf-tag-card > code { display: block; color: var(--epfl-red); font-weight: 800; }
.urdf-tag-card > strong { display: block; margin-top: 0.45rem; font-size: 1.2em; }
.urdf-tag-card pre { overflow: hidden; padding: 0.45rem; background: #f7f7f7; font-size: 0.72em; white-space: pre-wrap; }

.urdf-properties { display: grid; grid-template-columns: repeat(2, 1fr); gap: 0.55rem; }
.urdf-properties > div { padding: 0.6rem; border-top: 3px solid var(--black); background: #fafafa; }
.urdf-properties p { margin-bottom: 0; }

.challenge-strip,
.poe-extraction-flow {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.45rem;
  margin-top: var(--vgap-sm);
}
.challenge-strip span,
.poe-extraction-flow > div { padding: 0.55rem; border-top: 3px solid var(--black); background: #fafafa; }
.challenge-strip strong { color: var(--epfl-red); margin-right: 0.3rem; }
.poe-extraction-flow > div:nth-child(3) { border-top-color: var(--epfl-red); }
.poe-extraction-flow p { margin: 0.3rem 0 0; font-size: 0.9em; }

.representation-compare {
  flex: 1;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.7rem;
  min-height: 0;
}
.representation-compare article { padding: 0.8rem; border: 1px solid var(--line); border-top: 5px solid var(--black); }
.representation-compare article:nth-child(2) { border-top-color: var(--epfl-red); }
.representation-compare h3 { margin: 0 0 0.4rem; font-size: var(--font-h3); }
.mini-equation { padding: 0.45rem; background: #fafafa; font-size: 0.9em; }

.takeaway-stack { width: min(76rem, 100%); margin: auto; display: grid; gap: 0.65rem; }
.takeaway-row { display: grid; grid-template-columns: auto 1fr; gap: 0.75rem; align-items: start; }
.takeaway-number { color: var(--epfl-red); font-size: var(--font-h3); font-weight: 800; line-height: 1; }
.takeaway-row p { margin: 0.15rem 0 0; }

/* Shared interactive shell. */
.l2-demo {
  width: 100%;
  height: 100%;
  min-height: 0;
  display: grid;
  grid-template-columns: minmax(0, 1.55fr) minmax(18rem, 0.85fr);
  gap: 0.65rem;
  font-size: clamp(0.72rem, 0.82vw, 0.92rem);
}
.l2-stage { position: relative; min-width: 0; min-height: 0; overflow: hidden; border: 1px solid var(--line); background: #fafafa; }
.l2-stage canvas { display: block; width: 100%; height: 100%; }
.l2-stage-note { position: absolute; left: 0.55rem; bottom: 0.45rem; margin: 0; padding: 0.25rem 0.4rem; border-left: 2px solid var(--epfl-red); background: rgba(255,255,255,.88); color: var(--muted); pointer-events: none; }
.l2-panel { min-width: 0; min-height: 0; display: flex; flex-direction: column; gap: 0.45rem; }
.l2-card { padding: 0.55rem; border: 1px solid var(--line); background: var(--white); }
.l2-control { display: grid; grid-template-columns: 5.5rem 1fr 4rem; gap: 0.35rem; align-items: center; margin-top: 0.38rem; }
.l2-control label { font-weight: 700; }
.l2-control input[type="range"] { min-width: 0; width: 100%; }
.l2-control output { text-align: right; color: var(--muted); font-variant-numeric: tabular-nums; }
.l2-matrix { width: 100%; border-collapse: collapse; margin-top: 0.35rem; font-variant-numeric: tabular-nums; }
.l2-matrix td { padding: 0.2rem; border: 1px solid #e4e4e4; text-align: right; }
.l2-matrix td:last-child { background: #fafafa; font-weight: 700; }
.l2-vector { margin: 0.35rem 0 0; padding: 0.35rem; background: #fafafa; font-family: ui-monospace, monospace; font-variant-numeric: tabular-nums; }

.rotation2d-demo {
  width: 100%;
  height: 100%;
  min-height: 0;
  display: grid;
  grid-template-rows: minmax(13rem, 1fr) auto auto;
  gap: 0.42rem;
  font-size: clamp(0.72rem, 0.82vw, 0.92rem);
}
.rotation2d-canvas-wrap {
  position: relative;
  min-height: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  background: #fafafa;
}
.rotation2d-canvas-wrap canvas { display: block; width: 100%; height: 100%; }
.rotation2d-legend {
  position: absolute;
  left: 0.45rem;
  bottom: 0.35rem;
  margin: 0;
  padding: 0.25rem 0.35rem;
  background: rgba(255,255,255,.9);
  color: var(--muted);
  font-size: 0.88em;
}
.world-key { color: #666; font-weight: 800; }
.body-key { color: var(--epfl-red); font-weight: 800; }
.rotation2d-controls {
  display: grid;
  grid-template-columns: auto auto minmax(7rem, 1fr) 3.5rem;
  gap: 0.42rem;
  align-items: center;
}
.rotation2d-controls label { font-weight: 800; }
.rotation2d-controls input { width: 100%; }
.rotation2d-controls output { text-align: right; color: var(--muted); font-variant-numeric: tabular-nums; }
.rotation2d-readout {
  display: grid;
  grid-template-columns: auto minmax(10rem, 1fr);
  gap: 0.55rem;
  align-items: center;
  padding: 0.4rem 0.5rem;
  border: 1px solid var(--line);
}
.rotation2d-readout .l2-matrix { margin: 0; }

.poe-factor-strip { display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.25rem; margin-top: 0.4rem; }
.poe-factor { padding: 0.32rem; border-top: 2px solid var(--black); background: #fafafa; text-align: center; }
.poe-factor.is-active { border-top-color: var(--epfl-red); }
.poe-ghost-control {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 0.4rem;
  align-items: center;
  margin-top: 0.5rem;
  padding-top: 0.45rem;
  border-top: 1px solid var(--line);
  cursor: pointer;
  font-weight: 700;
}
.poe-ghost-control input { accent-color: var(--epfl-red); }
.poe-ghost-control output { color: var(--muted); font-variant-numeric: tabular-nums; }
.poe-model-status { margin: 0.3rem 0 0; color: var(--muted); font-size: 0.82em; }

.urdf-editor-demo { grid-template-columns: minmax(24rem, 1fr) minmax(0, 1fr); }
.urdf-editor-pane { min-width: 0; min-height: 0; display: grid; grid-template-rows: auto 1fr auto; gap: 0.35rem; }
.urdf-editor-toolbar { display: flex; justify-content: space-between; gap: 0.7rem; align-items: center; }
.urdf-upload-button { position: relative; overflow: hidden; margin: 0; padding: 0.34rem 0.7rem; cursor: pointer; }
.urdf-upload-button input { position: absolute; width: 1px; height: 1px; opacity: 0; pointer-events: none; }
.urdf-editor-pane textarea {
  width: 100%;
  height: 100%;
  min-height: 0;
  resize: none;
  padding: 0.55rem;
  border: 1px solid var(--line);
  font: 0.72em/1.32 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  tab-size: 2;
}
.urdf-editor-status { margin: 0; min-height: 1.4em; color: var(--muted); }
.urdf-editor-status.is-error { color: var(--epfl-red); font-weight: 700; }
.urdf-frame-controls { display: grid; grid-template-columns: 1fr; gap: 0.4rem; }
.urdf-frame-controls .l2-control { grid-template-columns: minmax(5rem, auto) 1fr 3.4rem; margin: 0; }

@media (max-width: 900px) {
  .lecture-02-title { white-space: normal; }
  .representation-path { grid-template-columns: 1fr; }
  .representation-arrow { transform: rotate(90deg); text-align: center; }
  .notation-grid,
  .notation-grid.compact,
  .representation-compare,
  .challenge-strip,
  .poe-extraction-flow { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .rodrigues-meaning,
  .adjoint-uses { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .adjoint-layout { grid-template-columns: 1fr; }
  .l2-demo,
  .urdf-editor-demo { grid-template-columns: 1fr; grid-template-rows: minmax(18rem, 1fr) auto; }
}