.rack-lesson {
  --rack-ink: #162535;
  --rack-muted: #596b7b;
  --rack-line: #d8e0e7;
  --rack-blue: #194bf0;
  --rack-soft-blue: #eef3ff;
  --rack-stage: #e9eef2;
  width: 100%;
  min-width: 0;
  margin: 8px 0 48px;
  overflow: hidden;
  color: var(--rack-ink);
  background: #fff;
  border: 1px solid var(--rack-line);
  border-radius: 6px;
  box-shadow: 0 8px 26px rgb(19 34 48 / 4%);
  text-align: left;
}

.rack-lesson *,
.rack-lesson *::before,
.rack-lesson *::after { box-sizing: border-box; }
.rack-lesson :is(h2, h3, p, figure, dl, dd) { margin: 0; }
.rack-lesson [hidden] { display: none !important; }
.rack-lesson button { font: inherit; cursor: pointer; touch-action: manipulation; }
.rack-lesson button:focus-visible { outline: 3px solid var(--rack-blue); outline-offset: 3px; }
.rack-lesson .rack-lesson__view-chip,.rack-lesson .rack-lesson__stage-reference { display:none; }
.rack-lesson__image-link { display:block; width:100%; }
.rack-lesson__full-size { display:inline-block; margin-top:8px; font-size:12px; color:var(--rack-blue); }
.rack-lesson__masthead {
  min-height: 58px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 16px 26px;
  border-bottom: 1px solid var(--rack-line);
}
.rack-lesson .rack-lesson__eyebrow {
  display: flex;
  align-items: center;
  gap: 9px;
  color: var(--rack-blue);
  font: 600 10px/1.5 var(--mono, ui-monospace, monospace);
  letter-spacing: .095em;
}
.rack-lesson__eyebrow-mark { width: 6px; height: 6px; background: var(--rack-blue); flex: 0 0 auto; }
.rack-lesson__example-tag { color: var(--rack-muted); font-size: 11px; line-height: 1.5; }
.rack-lesson__layout { display: grid; grid-template-columns: 285px minmax(0, 1fr); }
.rack-lesson__sidebar { min-width: 0; padding: 29px 24px 28px; border-right: 1px solid var(--rack-line); }
.rack-lesson .rack-lesson__introduction h2 {
  font-size: clamp(26px, 2.5vw, 32px);
  font-weight: 650;
  letter-spacing: -.045em;
  line-height: 1.1;
  margin-bottom: 15px;
}
.rack-lesson__introduction > p { color: var(--rack-muted); font-size: 13px; line-height: 1.65; }
.rack-lesson__view-controls { display: none; flex-direction: column; gap: 7px; margin: 28px -9px 29px; }
.rack-lesson.is-enhanced .rack-lesson__view-controls { display: flex; }
.rack-lesson__view-button {
  display: grid;
  grid-template-columns: 24px minmax(0, 1fr) 15px;
  align-items: start;
  width: 100%;
  min-height: 76px;
  gap: 8px;
  padding: 13px 9px;
  border: 1px solid transparent;
  border-radius: 4px;
  background: transparent;
  color: var(--rack-ink);
  text-align: left;
  transition: background-color 140ms, border-color 140ms;
}
.rack-lesson__view-button:hover { background: #f4f7fa; border-color: #e5ebf0; }
.rack-lesson__view-button[aria-pressed="true"] { background: var(--rack-soft-blue); border-color: #d5dfff; }
.rack-lesson__view-number { padding-top: 2px; color: #637687; font: 500 11px/1.55 var(--mono, ui-monospace, monospace); }
.rack-lesson__view-label { display: block; min-width: 0; }
.rack-lesson__view-label strong { display: block; font-size: 12px; font-weight: 650; line-height: 1.5; letter-spacing: -.01em; }
.rack-lesson__view-label > span:not(.rack-lesson__sr-only) { display: block; margin-top: 3px; color: var(--rack-muted); font-size: 10.5px; line-height: 1.55; }
.rack-lesson__view-arrow { margin-top: 2px; color: #8798a6; }
.rack-lesson__view-button[aria-pressed="true"] :is(.rack-lesson__view-number, strong, .rack-lesson__view-arrow) { color: var(--rack-blue); }
.rack-lesson__explanations { border-top: 1px solid var(--rack-line); margin-top: 26px; padding-top: 23px; }
.rack-lesson.is-enhanced .rack-lesson__explanations { margin-top: 0; }
.rack-lesson__small-label { display: block; margin-bottom: 12px; color: var(--rack-muted); font: 500 9px/1.5 var(--mono, ui-monospace, monospace); letter-spacing: .08em; }
.rack-lesson .rack-lesson__explanation h3 { font-size: 15px; font-weight: 650; line-height: 1.35; letter-spacing: -.015em; margin-bottom: 10px; }
.rack-lesson__explanation > p { font-size: 12px; line-height: 1.7; color: #465c6e; }
.rack-lesson__explanation strong { font-weight: 650; color: var(--rack-ink); }
.rack-lesson .rack-lesson__takeaway { margin-top: 13px; color: var(--rack-muted); }
.rack-lesson__mistake-button {
  display: none;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 42px;
  width: 100%;
  margin-top: 20px;
  padding: 9px 11px;
  border: 1px solid #b9c8d5;
  border-radius: 3px;
  background: #fff;
  color: var(--rack-ink);
  font-size: 12px !important;
  font-weight: 600 !important;
}
.rack-lesson.is-enhanced .rack-lesson__mistake-button { display: inline-flex; }
.rack-lesson__mistake-button:hover { color: var(--rack-blue); border-color: var(--rack-blue); }
.rack-lesson__mistake-button[aria-pressed="true"] { background: #fff7eb; border-color: #d5a75c; color: #774812; }
.rack-lesson__visual { min-width: 0; align-self: start; background: #f8fafb; }
.rack-lesson__figure { min-width: 0; }
.rack-lesson__stage { position: relative; display: grid; isolation: isolate; min-width: 0; aspect-ratio: 5 / 4; overflow: hidden; background: var(--rack-stage); }
.rack-lesson #rack-position-image { display: block; width: 100%; height: 100%; max-width: 100%; object-fit: contain; grid-area: 1 / 1; }
.rack-lesson__view-chip {
  position: absolute;
  top: 20px;
  left: 22px;
  z-index: 2;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  max-width: calc(100% - 44px);
  padding: 7px 9px;
  border: 1px solid rgb(171 188 201 / 50%);
  border-radius: 3px;
  background: rgb(255 255 255 / 92%);
  color: #4b6276;
  font: 500 9px/1.5 var(--mono, ui-monospace, monospace);
  letter-spacing: .045em;
}
.rack-lesson__view-chip > span:first-child { width: 5px; height: 5px; background: var(--rack-blue); border-radius: 50%; flex-shrink: 0; }
.rack-lesson__stage-reference { position: absolute; bottom: 16px; left: 22px; color: #586c7e; font: 500 9px/1.5 var(--mono, ui-monospace, monospace); letter-spacing: .06em; }
.rack-lesson__annotations { position: absolute; inset: 0; z-index: 1; pointer-events: none; }
.rack-lesson__caption { display: flex; align-items: flex-start; gap: 13px; min-height: 82px; padding: 20px 23px; background: #fff; border-top: 1px solid var(--rack-line); }
.rack-lesson__caption-mark { display: grid; place-items: center; flex: 0 0 27px; width: 27px; height: 29px; margin-top: 1px; background: var(--rack-soft-blue); border: 1px solid #dce5ff; border-radius: 3px; color: var(--rack-blue); }
.rack-lesson__caption p { color: #526778; font-size: 12px; line-height: 1.65; }
.rack-lesson__caption strong { color: var(--rack-ink); font-weight: 600; }
.rack-lesson__record { margin: 0; padding: 21px 23px 22px; border-top: 1px solid var(--rack-line); background: #f7f9fc; }
.rack-lesson.is-enhanced:not([data-rack-active-view="record"]) .rack-lesson__record { display: none; }
.rack-lesson__record-heading { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 19px; }
.rack-lesson .rack-lesson__record-heading h3 { font-size: 13px; font-weight: 650; letter-spacing: -.01em; line-height: 1.4; }
.rack-lesson__record-status { font-size: 10px; line-height: 1.5; color: #385777; text-align: right; }
.rack-lesson__record-fields { display: grid; grid-template-columns: 1.12fr 1.1fr 1fr; gap: 17px 18px; }
.rack-lesson__record-field { min-width: 0; }
.rack-lesson__record-field dt { margin-bottom: 4px; font-size: 10px; line-height: 1.5; color: var(--rack-muted); }
.rack-lesson__record-field dd { color: var(--rack-ink); font: 600 12px/1.5 var(--mono, ui-monospace, monospace); overflow-wrap: anywhere; }
.rack-lesson__record-field--position dd { color: var(--rack-blue); }
.rack-lesson__position-unit { display: block; margin-top: 2px; font: 10px/1.5 Inter, "Segoe UI", Arial, sans-serif; color: var(--rack-muted); }
.rack-lesson .rack-lesson__record-note { margin-top: 18px; padding-top: 12px; border-top: 1px solid var(--rack-line); font-size: 11px; line-height: 1.6; color: #526778; }
.rack-lesson[data-rack-mistake="true"] .rack-lesson__record,
.rack-lesson.is-mistake .rack-lesson__record { background: #fff9ef; }
.rack-lesson[data-rack-mistake="true"] :is([data-rack-position-value], [data-rack-record-status], [data-rack-mistake-note]),
.rack-lesson.is-mistake :is([data-rack-position-value], [data-rack-record-status], [data-rack-mistake-note]) { color: #8a4815; }
.rack-lesson__scope { display: grid; grid-template-columns: 237px minmax(0, 1fr); gap: 24px; align-items: start; padding: 17px 24px; border-top: 1px solid var(--rack-line); background: #f8fafc; }
.rack-lesson__scope-label { padding-top: 2px; color: #5b6f82; font: 500 9px/1.5 var(--mono, ui-monospace, monospace); letter-spacing: .075em; }
.rack-lesson__scope p { color: var(--rack-muted); font-size: 10.5px; line-height: 1.65; }
.rack-lesson__print-views { display: none; }
.rack-lesson__sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; border: 0; }

@media (min-width: 1200px) {
  .rack-lesson__sidebar { padding-top: 34px; }
  .rack-lesson__introduction > p { font-size: 13.5px; }
  .rack-lesson__view-label strong { font-size: 12.5px; }
  .rack-lesson__view-label > span:not(.rack-lesson__sr-only) { font-size: 11px; }
  .rack-lesson__explanation > p { font-size: 12.5px; }
}

@media (max-width: 900px) {
  .rack-lesson__layout { grid-template-columns: 250px minmax(0, 1fr); }
  .rack-lesson__sidebar { padding: 26px 19px; }
  .rack-lesson__stage { aspect-ratio: 1.12; }
  .rack-lesson__scope { grid-template-columns: 207px minmax(0, 1fr); gap: 24px; padding-inline: 19px; }
  .rack-lesson__record-fields { grid-template-columns: 1fr 1fr; }
  .rack-lesson__record-heading { align-items: flex-start; flex-direction: column; gap: 4px; }
}

@media (max-width: 700px) {
  .rack-lesson { margin-bottom: 34px; }
  .rack-lesson__masthead { min-height: 48px; padding: 13px 17px; gap: 10px; }
  .rack-lesson .rack-lesson__eyebrow { font-size: 9px; gap: 7px; letter-spacing: .05em; }
  .rack-lesson__example-tag { font-size: 9px; }
  .rack-lesson__layout { display: flex; flex-direction: column; }
  .rack-lesson__sidebar { display: contents; }
  .rack-lesson__introduction { order: 1; padding: 22px 20px 18px; }
  .rack-lesson .rack-lesson__introduction h2 { font-size: 28px; line-height: 1.1; margin-bottom: 10px; }
  .rack-lesson__introduction h2 br { display: none; }
  .rack-lesson__introduction h2 br::after { content: " "; }
  .rack-lesson__introduction > p { font-size: 12px; line-height: 1.65; max-width: 520px; }
  .rack-lesson__view-controls { order: 2; margin: 0; padding: 0 13px 16px; gap: 6px; }
  .rack-lesson.is-enhanced .rack-lesson__view-controls { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); }
  .rack-lesson__view-button { display: flex; flex-direction: column; gap: 6px; min-height: 93px; height: 100%; padding: 10px; border-color: #e4eaf0; background: #fbfcfd; }
  .rack-lesson__view-number { padding: 0; font-size: 10px; line-height: 1.4; }
  .rack-lesson__view-label strong { font-size: 10.5px; line-height: 1.45; font-weight: 600; }
  .rack-lesson__view-label > span:not(.rack-lesson__sr-only),
  .rack-lesson__view-arrow { display: none; }
  .rack-lesson__visual { order: 3; width: 100%; border-top: 1px solid var(--rack-line); }
  .rack-lesson__stage { aspect-ratio: 1.12; }
  .rack-lesson__view-chip { left: 15px; top: 15px; max-width: calc(100% - 30px); font-size: 8px; padding: 6px 8px; }
  .rack-lesson__stage-reference { left: 15px; bottom: 12px; font-size: 8px; }
  .rack-lesson__caption { padding: 17px 18px; gap: 11px; min-height: 0; }
  .rack-lesson__caption p { font-size: 11px; line-height: 1.65; }
  .rack-lesson__explanations,
  .rack-lesson.is-enhanced .rack-lesson__explanations { order: 4; margin: 0; padding: 20px; border-top: 1px solid var(--rack-line); }
  .rack-lesson__small-label { margin-bottom: 9px; }
  .rack-lesson .rack-lesson__explanation h3 { font-size: 16px; }
  .rack-lesson__explanation > p { font-size: 12px; }
  .rack-lesson__mistake-button { width: auto; min-width: 170px; }
  .rack-lesson__record { padding: 19px 20px; }
  .rack-lesson__record-heading { flex-direction: row; gap: 10px; }
  .rack-lesson__record-heading h3 { max-width: 160px; }
  .rack-lesson__record-status { max-width: 105px; }
  .rack-lesson__record-fields { gap: 17px 20px; }
  .rack-lesson__scope { display: block; padding: 17px 20px; }
  .rack-lesson__scope-label { display: block; margin-bottom: 6px; padding-top: 0; }
  .rack-lesson__scope p { font-size: 10px; }
}

@media (max-width: 390px) {
  .rack-lesson__masthead { flex-wrap: wrap; gap: 3px 10px; }
  .rack-lesson__example-tag { font-size: 8px; }
  .rack-lesson__view-controls { padding-inline: 11px; gap: 5px; }
  .rack-lesson__view-button { padding: 9px 7px; }
  .rack-lesson__view-label strong { font-size: 10px; }
  .rack-lesson .rack-lesson__introduction h2 { font-size: 26px; }
}

@media (prefers-reduced-motion: reduce) {
  .rack-lesson *, .rack-lesson *::before, .rack-lesson *::after { transition: none !important; animation: none !important; scroll-behavior: auto !important; }
}

@media print {
  .rack-lesson { overflow: visible; margin: 20px 0; box-shadow: none; border: 1px solid #aab5bf; border-radius: 0; break-inside: auto; color: #111; }
  .rack-lesson__masthead { padding: 10px 14px; min-height: 0; }
  .rack-lesson__layout { display: block; }
  .rack-lesson__sidebar { display: block; padding: 14px; border: 0; }
  .rack-lesson .rack-lesson__introduction h2 { font-size: 20pt; }
  .rack-lesson__introduction h2 br { display: none; }
  .rack-lesson__introduction > p { font-size: 9pt; }
  .rack-lesson.is-enhanced .rack-lesson__view-controls,
  .rack-lesson__view-controls,
  .rack-lesson__explanations,
  .rack-lesson__figure,
  .rack-lesson__record,
  .rack-lesson__mistake-button { display: none !important; }
  .rack-lesson__visual { border: 0; }
  .rack-lesson__scope { display: block; padding: 10px 14px; background: white; }
  .rack-lesson__scope-label { display: block; margin-bottom: 4px; }
  .rack-lesson__scope p { font-size: 8pt; }
  .rack-lesson__print-views { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 12px; padding: 14px; border-top: 1px solid var(--rack-line); }
  .rack-lesson__print-views figure { break-inside: avoid; }
  .rack-lesson__print-views img { display: block; width: 100%; height: auto; }
  .rack-lesson__print-views figcaption { margin-top: 7px; font-size: 7.5pt; line-height: 1.5; color: #111; }
}

/* Optional guided 3D keeps the static lesson available before and after use. */
.rack-lesson__3d-toolbar { display:none; padding:16px 20px; gap:10px; align-items:center; flex-wrap:wrap; background:#fff; border-bottom:1px solid var(--rack-line); }
.rack-lesson.is-enhanced .rack-lesson__3d-toolbar { display:flex; }
.rack-lesson__3d-toolbar button { border:1px solid #becbd8; border-radius:4px; padding:10px 13px; min-height:44px; background:#fff; color:var(--rack-ink); font-size:12px; font-weight:600; }
.rack-lesson__3d-toolbar [data-rack-3d] { color:#fff; background:var(--rack-blue); border-color:var(--rack-blue); }
.rack-lesson__3d-toolbar [data-rack-3d]:disabled { opacity:.6; cursor:wait; }
.rack-lesson__3d-toolbar [data-rack-live-controls] { display:flex; gap:6px; flex-wrap:wrap; }
.rack-lesson__3d-toolbar [data-rack-live-status] { flex-basis:100%; color:var(--rack-muted); font-size:11px; line-height:1.6; }
.rack-lesson__live { position:absolute; inset:0; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
.rack-lesson__live-heading { padding:22px 26px 8px; display:grid; gap:7px; }
.rack-lesson__live-heading span { color:var(--rack-blue); font:600 10px/1.4 var(--mono,monospace); letter-spacing:.08em; }
.rack-lesson__live-heading strong { font-size:clamp(17px,2vw,26px); line-height:1.25; }
.rack-lesson__canvas { min-width:0; min-height:0; overflow:hidden; }
.rack-lesson__canvas canvas { display:block; width:100%; height:100%; }
.rack-lesson__canvas canvas:focus-visible { outline:3px solid var(--rack-blue); outline-offset:-4px; }
.rack-lesson__live-facts { margin:0 24px; border-top:1px solid #cbd7e1; padding:13px 0 17px; display:grid; gap:5px; font-size:12px; }
.rack-lesson__live-facts span { color:var(--rack-muted); font-size:11px; }
.rack-lesson.is-enhanced.is-3d .rack-lesson__record { display:block; }
@media(max-width:700px){
 .rack-lesson.is-3d .rack-lesson__stage { aspect-ratio:auto; height:450px; }
 .rack-lesson__3d-toolbar { padding:14px; }
 .rack-lesson__3d-toolbar button { padding:9px 10px; }
 .rack-lesson__live-heading { padding:18px 18px 8px; }
 .rack-lesson__live-facts { margin:0 18px; }
}
@media print { .rack-lesson__3d-toolbar,.rack-lesson__live { display:none !important; } }