.nowrap { white-space: nowrap; }
.lesson-svg.lesson-mobile-drawing { display: none; }
.ceiling-lesson-page { max-width: 1120px; }
.ceiling-lesson-intro { max-width: 920px; margin-bottom: 24px; }
.ceiling-lesson-intro h1 { font-size: clamp(2.4rem, 5.4vw, 4.7rem); }
.ceiling-lesson-intro .lede { max-width: 860px; }
.lesson-flow {
  margin-top: 18px;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 9px;
  color: var(--muted);
  font-size: .82rem;
  font-weight: 760;
}
.lesson-flow span { display: inline-flex; align-items: center; gap: 7px; }
.lesson-flow strong {
  width: 25px; height: 25px; display: inline-grid; place-items: center;
  border-radius: 999px; background: var(--dark); color: var(--accent); font-size: .72rem;
}
.lesson-top-actions { margin-top: 17px; display: flex; flex-wrap: wrap; gap: 9px; }
.lesson-top-actions .subtle-button { text-decoration: none; }
.lesson-jump {
  margin: 0 0 18px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
}
.lesson-jump a {
  padding: 7px 9px;
  border-radius: 9px;
  color: var(--muted);
  text-decoration: none;
  font-size: .76rem;
  font-weight: 790;
}
.lesson-jump a:hover { background: var(--bg); color: var(--text); }
.lesson-section {
  margin-top: 18px;
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 20px;
  background: #fff;
}
.lesson-section-head { display: grid; grid-template-columns: auto minmax(0, 1fr); gap: 16px; align-items: start; margin-bottom: 19px; }
.lesson-section-head h2 { margin: 0 0 8px; font-size: clamp(1.55rem, 3vw, 2.15rem); letter-spacing: -.035em; }
.lesson-section-head p { margin: 0; max-width: 840px; color: var(--muted); line-height: 1.58; }
.lesson-step {
  min-width: 66px;
  padding: 8px 9px;
  border-radius: 999px;
  background: var(--dark);
  color: var(--accent);
  font-size: .66rem;
  font-weight: 900;
  letter-spacing: .08em;
  text-align: center;
}
.lesson-visual-card {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #f8f9f5;
}
.lesson-visual-heading {
  padding: 13px 15px;
  border-bottom: 1px solid var(--line);
  background: #fff;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.lesson-visual-heading span, .lesson-compare-label {
  color: var(--muted);
  font-size: .66rem;
  font-weight: 900;
  letter-spacing: .09em;
}
.lesson-visual-heading strong { font-size: .83rem; }
.lesson-svg { width: 100%; height: auto; display: block; font-family: Inter, ui-sans-serif, system-ui, sans-serif; }
.lesson-svg .room-outline { fill: #fff; stroke: #1c211a; stroke-width: 3; }
.lesson-svg .full-tile-gray rect { fill: #d9dcd5; stroke: #aeb3aa; stroke-width: 1.5; }
.lesson-svg .tile-fill rect { fill: #fff; stroke: #afb5aa; stroke-width: 1.25; }
.lesson-svg .tile-grid-lines line { stroke: #939a8e; stroke-width: 1.5; }
.lesson-svg .cross-grid-lines line { stroke: #c5cac1; stroke-width: 1.2; }
.lesson-svg .leftover-fill, .lesson-svg .border-fill { fill: #e5ff50; stroke: #bdcf35; stroke-width: 1.5; }
.lesson-svg .center-tile-fill { fill: #f4ffc2 !important; stroke: #9cab2c !important; stroke-width: 2 !important; }
.lesson-svg .dim-line { stroke: #6d716a; stroke-width: 2; }
.lesson-svg .witness { stroke: #a4aaa0; stroke-width: 1.5; }
.lesson-svg .dim-text, .lesson-svg .center-label, .lesson-svg .rule-result-text, .lesson-svg .compare-cut-text {
  fill: #181a17; font-size: 16px; font-weight: 850; text-anchor: middle;
}
.lesson-svg .tile-label { fill: #4f554c; font-size: 17px; font-weight: 900; text-anchor: middle; }
.lesson-svg .tile-label-small { fill: #6d716a; font-size: 14px; font-weight: 700; text-anchor: middle; }
.lesson-svg .tile-count-text text { fill: #4f554c; font-size: 20px; font-weight: 900; text-anchor: middle; dominant-baseline: middle; }
.lesson-svg .rule-helper-text { fill: #6d716a; font-size: 14px; font-weight: 760; text-anchor: middle; }
.lesson-svg .leftover-label { fill: #3f4616; font-size: 13px; font-weight: 900; text-anchor: middle; }
.lesson-svg .visual-caption { fill: #6d716a; font-size: 13px; font-weight: 760; text-anchor: start; }
.lesson-svg .visual-caption-right { text-anchor: end; }
.lesson-svg .center-line { stroke: #181a17; stroke-width: 3; stroke-dasharray: 7 6; }
.lesson-svg .border-label { fill: #3f4616; font-size: 13px; font-weight: 900; text-anchor: middle; }
.lesson-svg .center-result { fill: #4f554c; font-size: 14px; font-weight: 850; text-anchor: middle; }
.lesson-math-row, .lesson-equation, .lesson-why-12 {
  margin-top: 14px;
  padding: 13px 15px;
  border: 1px solid var(--line);
  border-radius: 13px;
  background: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 12px;
}
.lesson-math-row div { min-width: 150px; display: grid; gap: 3px; text-align: center; }
.lesson-math-row span { color: var(--muted); font-size: .7rem; font-weight: 760; }
.lesson-math-row strong { font-size: 1.2rem; }
.lesson-math-row b, .lesson-equation b, .lesson-why-12 b { color: #969c92; }
.lesson-math-result { padding: 8px 12px; border-radius: 10px; background: var(--accent-soft); }
.lesson-equation, .lesson-why-12 { margin-bottom: 14px; background: #f8f9f5; font-size: .9rem; }
.lesson-equation strong, .lesson-why-12 strong { padding: 7px 10px; border-radius: 9px; background: var(--accent); }
.lesson-equation-accent { background: var(--accent-soft); border-color: #dce887; }
.lesson-plain-note {
  margin: 14px 0 0;
  padding: 13px 15px;
  border-left: 4px solid var(--accent);
  background: #f8f9f5;
  color: var(--muted);
  line-height: 1.55;
  font-size: .86rem;
}
.lesson-rule-grid, .lesson-compare-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.lesson-rule-card, .lesson-compare-card {
  padding: 17px;
  border: 1px solid var(--line);
  border-radius: 15px;
  background: #f8f9f5;
}
.lesson-rule-card h3, .lesson-compare-card h3 { margin: 8px 0 5px; font-size: 1.12rem; }
.lesson-rule-card p, .lesson-compare-card p { margin: 0; color: var(--muted); font-size: .82rem; line-height: 1.48; }
.rule-badge {
  display: inline-flex; padding: 5px 7px; border-radius: 7px;
  background: var(--dark); color: var(--accent); font-size: .62rem; font-weight: 900; letter-spacing: .08em;
}
.lesson-memory-rule {
  margin-top: 14px;
  padding: 15px 16px;
  border-radius: 14px;
  background: var(--dark);
  color: #fff;
  display: grid;
  grid-template-columns: auto 1fr 1fr;
  align-items: center;
  gap: 14px;
}
.lesson-memory-rule strong { color: var(--accent); }
.lesson-memory-rule span { font-size: .82rem; }
.lesson-memory-rule b { color: var(--accent); }
.lesson-compare-card-accent { border-color: #dce887; background: var(--accent-soft); }
.lesson-equal-grid { display: grid; grid-template-columns: 1fr auto 1fr; gap: 14px; align-items: center; margin-bottom: 14px; }
.lesson-equal-card { padding: 18px; border: 1px solid var(--line); border-radius: 15px; background: #f8f9f5; }
.lesson-equal-card > span { color: var(--muted); font-size: .7rem; font-weight: 850; letter-spacing: .05em; }
.lesson-equal-card h3 { margin: 5px 0 12px; font-size: 1.25rem; }
.lesson-mini-math { margin-top: 7px; padding: 8px 9px; border-radius: 9px; background: #fff; font-size: .8rem; }
.lesson-equal-card p { margin: 12px 0 0; color: var(--muted); font-size: .82rem; }
.lesson-equal-card-accent { background: var(--accent-soft); border-color: #dce887; }
.lesson-equal-arrow { color: #969c92; font-size: 1.4rem; font-weight: 900; }
.lesson-equal-visuals { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); }
.lesson-equal-visuals > div + div { border-left: 1px solid var(--line); }
.lesson-visual-subtitle { display: block; padding: 12px 14px 0; color: var(--muted); font-size: .72rem; font-weight: 850; text-align: center; }

.lesson-process-list {
  margin: 0;
  padding-left: 1.25rem;
  max-width: 860px;
  display: grid;
  gap: 9px;
  color: var(--muted);
  line-height: 1.58;
}
.lesson-process-list li { padding-left: 3px; }
.lesson-process-list strong { color: var(--text); }
.lesson-center-equation { margin-bottom: 14px; }
.lesson-pattern-block {
  margin-top: 14px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
}
.lesson-pattern-head {
  padding: 13px 15px;
  border-bottom: 1px solid var(--line);
  background: #f8f9f5;
  display: grid;
  gap: 3px;
}
.lesson-pattern-head strong { font-size: .9rem; }
.lesson-pattern-head span { color: var(--muted); font-size: .78rem; line-height: 1.4; }
.lesson-pattern-table {
  width: 100%;
  border-collapse: collapse;
  table-layout: fixed;
  font-size: .8rem;
}
.lesson-pattern-table caption {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}
.lesson-pattern-table th,
.lesson-pattern-table td {
  padding: 10px 9px;
  border-bottom: 1px solid var(--line);
  text-align: center;
  vertical-align: middle;
}
.lesson-pattern-table th {
  background: #fff;
  color: var(--muted);
  font-size: .68rem;
  font-weight: 900;
  letter-spacing: .035em;
}
.lesson-pattern-table th:nth-child(1), .lesson-pattern-table td:nth-child(1) { width: 25%; }
.lesson-pattern-table th:nth-child(2), .lesson-pattern-table td:nth-child(2) { width: 15%; }
.lesson-pattern-table th:nth-child(3), .lesson-pattern-table td:nth-child(3) { width: 20%; }
.lesson-pattern-table th:nth-child(4), .lesson-pattern-table td:nth-child(4) { width: 40%; }
.lesson-pattern-table tbody tr:nth-child(even) { background: #f8f9f5; }
.lesson-pattern-table tbody tr:last-child td { border-bottom: 0; }
.lesson-pattern-table td:first-child,
.lesson-pattern-table td:nth-child(2) { font-weight: 850; }

.lesson-summary-card {
  margin-top: 18px;
  padding: 24px;
  border-radius: 18px;
  background: var(--dark);
  color: #fff;
}
.lesson-summary-card .section-kicker { color: var(--accent); }
.lesson-summary-card h2 { margin: 0 0 15px; color: #fff; }
.lesson-summary-card ol { margin: 0; padding-left: 23px; display: grid; gap: 10px; }
.lesson-summary-card li { padding-left: 5px; line-height: 1.5; color: #e6e9e2; }
.lesson-summary-card strong { color: #fff; }
.lesson-next { margin-top: 18px; padding: 22px; border: 1px solid var(--line); border-radius: 18px; background: #fff; }
.lesson-next-head h2 { margin-bottom: 14px; }
.lesson-next-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 10px; }
.lesson-next-grid a {
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 13px;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 11px;
  color: var(--text);
  text-decoration: none;
}
.lesson-next-grid a:hover { border-color: #b8bdb0; background: #f8f9f5; }
.lesson-next-grid a > span { width: 33px; height: 33px; display: grid; place-items: center; border-radius: 10px; background: var(--dark); color: var(--accent); font-weight: 900; }
.lesson-next-grid div { display: grid; gap: 2px; }
.lesson-next-grid small { color: var(--muted); line-height: 1.35; }
.lesson-next-grid b { font-size: 1.2rem; }

@media (max-width: 760px) {
  .ceiling-lesson-intro h1 { font-size: clamp(2.05rem, 10.2vw, 3.1rem); line-height: 1.06; }
  .ceiling-lesson-intro { margin-bottom: 16px; }
  .lesson-flow {
    margin-top: 14px;
    display: grid;
    grid-template-columns: 1fr;
    gap: 8px;
    font-size: .78rem;
  }
  .lesson-flow > span[aria-hidden="true"] { display: none; }
  .lesson-flow > span:not([aria-hidden="true"]) { width: 100%; padding: 7px 0; }
  .lesson-jump { overflow-x: auto; flex-wrap: nowrap; -webkit-overflow-scrolling: touch; }
  .lesson-jump a { flex: 0 0 auto; }
  .lesson-section { padding: 16px 12px; border-radius: 16px; }
  .lesson-section-head { grid-template-columns: 1fr; gap: 10px; }
  .lesson-step { justify-self: start; }
  .lesson-visual-heading { align-items: flex-start; flex-direction: column; gap: 4px; }
  .lesson-desktop-drawing { display: none; }
  .lesson-svg.lesson-mobile-drawing { display: block; width: 100%; max-width: 520px; margin: 0 auto; }
  .lesson-svg-long { min-width: 0; }
  .lesson-visual-card { overflow: hidden; }
  .lesson-svg-rule, .lesson-svg-compare, .lesson-svg-equal { min-width: 0; width: 100%; }
  .lesson-rule-card, .lesson-compare-card { overflow: visible; }
  .lesson-math-row { display: grid; grid-template-columns: 1fr; gap: 7px; }
  .lesson-math-row b { transform: none; justify-self: center; }
  .lesson-rule-grid, .lesson-compare-grid, .lesson-next-grid, .lesson-equal-visuals { grid-template-columns: 1fr; }
  .lesson-memory-rule { grid-template-columns: 1fr; gap: 8px; }
  .lesson-equal-grid { grid-template-columns: 1fr; }
  .lesson-equal-arrow { transform: rotate(90deg); justify-self: center; }
  .lesson-equal-visuals > div + div { border-left: 0; border-top: 1px solid var(--line); }
  .lesson-equation, .lesson-why-12 { align-items: stretch; flex-direction: column; text-align: center; gap: 7px; }
  .lesson-equation b, .lesson-why-12 b { transform: none; }
  .lesson-equation b.lesson-down-arrow, .lesson-why-12 b.lesson-down-arrow { transform: rotate(90deg); align-self: center; }

  .lesson-process-list { padding-left: 1.15rem; gap: 8px; font-size: .9rem; }
  .lesson-pattern-head { padding: 11px 10px; }
  .lesson-pattern-table { font-size: .72rem; }
  .lesson-pattern-table th, .lesson-pattern-table td { padding: 8px 4px; }
  .lesson-pattern-table th { font-size: .61rem; letter-spacing: 0; line-height: 1.2; }
  .lesson-mobile-drawing .dim-text { font-size: 17px; }
  .lesson-mobile-drawing .mobile-drawing-label { fill: #4f554c; font-size: 15px; font-weight: 900; text-anchor: middle; }
  .lesson-mobile-drawing .mobile-drawing-sub { fill: #6d716a; font-size: 12px; font-weight: 760; text-anchor: middle; }
  .lesson-mobile-drawing .mobile-cut-label { fill: #3f4616; font-size: 10px; font-weight: 900; text-anchor: middle; }
  .lesson-mobile-drawing .mobile-caption { fill: #6d716a; font-size: 12px; font-weight: 760; text-anchor: middle; }
  .lesson-mobile-drawing .mobile-caption-strong { fill: #181a17; font-weight: 900; }
}

@media (max-width: 500px) {
  .lesson-top-actions { align-items: stretch; flex-direction: column; }
  .lesson-top-actions .subtle-button { width: 100%; text-align: center; }
  .lesson-svg-rule, .lesson-svg-compare, .lesson-svg-equal { min-width: 0; width: 100%; }
  .lesson-rule-card, .lesson-compare-card { overflow: visible; }
}

.lesson-plain-note-emphasis { background: #f8f9f5; border: 1px solid var(--line); padding: 12px 14px; border-radius: 12px; }
.lesson-pro-tip-card {
  margin-top: 26px;
  background: #fff;
  color: var(--text);
  border: 1px solid var(--line);
  box-shadow: none;
}
.lesson-pro-tip-card .section-kicker {
  display: inline-flex;
  width: fit-content;
  margin-bottom: 8px;
  padding: 5px 8px;
  border-radius: 7px;
  background: var(--accent);
  color: var(--dark);
}
.lesson-pro-tip-card h2 { color: var(--text); }
.lesson-pro-tip-card > p:not(.section-kicker):not(.lesson-plain-note) {
  color: var(--muted);
  line-height: 1.58;
}
.lesson-pro-list { margin: 12px 0 14px 20px; padding: 0; color: var(--text); }
.lesson-pro-list li { margin: 8px 0; line-height: 1.45; }
.lesson-pro-tip-card .lesson-plain-note {
  margin-top: 14px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--accent);
  background: #f8f9f5;
  color: var(--muted);
}
.lesson-pro-tip-card .lesson-plain-note strong { color: var(--text); }

.lesson-field-note {
  margin-top: 26px;
  padding: 22px 24px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--accent);
  border-radius: 18px;
  background: #fff;
  color: var(--text);
}
.lesson-field-note .section-kicker {
  display: inline-flex;
  margin: 0 0 10px;
  padding: 5px 8px;
  border-radius: 7px;
  background: var(--accent);
  color: var(--dark);
}
.lesson-field-note h2 {
  margin: 0 0 10px;
  color: var(--text);
}
.lesson-field-note p {
  margin: 8px 0 0;
  color: var(--muted);
  line-height: 1.58;
}
.lesson-field-note strong { color: var(--text); }