/* Desktop content-height baseline: 1280 × 720. Mobile uses natural flow. */
.about-page .launch{min-height:900px}
.about-page .intro{min-height:650px}
.about-page .about-notes{min-height:480px}
.about-page .about-end{min-height:330px}
.about-page .info-header{height:72px}
.chapter-nav{position:sticky;top:72px;z-index:20;display:flex;min-height:52px;justify-content:center;align-items:center;gap:30px;padding:4px var(--about-pad);border-block:1px solid var(--about-rule);background:#fff;overflow-x:auto;overscroll-behavior-inline:contain}
.chapter-nav a{display:inline-flex;min-height:44px;align-items:center;flex:none;color:#4e5968;font-size:12px;font-weight:600}
.chapter-nav a:hover{color:var(--about-blue)}
.long-chapter{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);min-height:820px;align-items:center;gap:clamp(30px,6vw,86px);padding:86px var(--about-pad);border-bottom:1px solid var(--about-rule)}
.long-chapter[id],#formula-lab{scroll-margin-top:144px}
.chapter-caption{margin:0 0 22px;color:var(--about-blue);font-size:13px;font-weight:700}
.chapter-copy h2{margin:0 0 28px;color:#191f28;font-size:clamp(34px,4.3vw,62px);font-weight:800;line-height:1.22;letter-spacing:-.075em}
.chapter-copy>p:not(.chapter-caption){margin:0 0 18px;color:#4e5968;font-size:16px;line-height:1.95}
.chapter-copy>p:last-child{margin-bottom:0}
.chapter-link{display:inline-flex;min-height:44px;align-items:center;color:var(--about-blue);font-size:14px;font-weight:700}
.chapter-link:hover{text-decoration:underline;text-underline-offset:4px}
.math-type{font-family:Georgia,"Times New Roman",serif;font-weight:400;font-variant-numeric:lining-nums tabular-nums}
.thought-sheet{padding:40px 34px;border-block:2px solid #2c4d7c;background:#f6f9ff}
.thought-sheet>p{margin:0 0 30px;color:#64748b;font-size:14px}
.thought-sheet>div{display:grid;gap:8px;padding:24px 0;border-top:1px solid #d8e3f4}
.thought-sheet>div span{color:#6b7b93;font-size:12px}
.thought-sheet strong{color:#244979;font-size:23px;font-weight:600;letter-spacing:-.04em}
.thought-sheet strong.math-type{font-size:36px;font-weight:400}
.thought-sheet a{display:inline-flex;min-height:44px;align-items:center;gap:16px;margin-top:12px;color:#1557d4;font-size:14px;font-weight:700}
.domain-chapter,.science-chapter,.record-chapter,.collection-chapter{background:#f6f8fb}
.domain-index{border-top:2px solid #191f28}
.domain-index a{position:relative;display:grid;gap:7px;padding:25px 34px 25px 0;border-bottom:1px solid #d5dce6}
.domain-index span{color:#1557d4;font-size:12px;font-weight:700}
.domain-index strong{color:#191f28;font-size:22px;font-weight:700;letter-spacing:-.05em}
.domain-index small{color:#64748b;font-size:12px}
.domain-index b{position:absolute;top:48%;right:5px;color:#1557d4;font-weight:400}
.domain-index a:hover strong{color:#1557d4}
.search-demo{min-width:0}
.search-demo form label{display:block;margin-bottom:12px;color:#293f5b;font-size:15px;font-weight:700}
.search-demo form>div{display:flex;min-width:0;border:2px solid #1557d4;border-radius:8px;overflow:hidden;background:#fff}
.search-demo form>div:focus-within{outline:2px solid #1557d4;outline-offset:4px}
.search-demo input{width:100%;min-width:0;min-height:58px;padding:12px 16px;border:0;font:inherit;color:#191f28;background:#fff}
.search-demo button{flex:none;min-width:82px;padding-inline:13px;border:0;background:#1557d4;color:#fff;font-weight:700;cursor:pointer}
.search-demo .demo-caption{margin:12px 0;color:#64748b;font-size:12px;line-height:1.8}
.search-suggestions{display:flex;flex-wrap:wrap;gap:8px 20px}
.search-suggestions a{display:inline-flex;min-height:44px;align-items:center;color:#1557d4;font-size:13px}
.search-steps{margin:30px 0 0;padding:0;list-style:none}
.search-steps li{display:flex;gap:20px;padding:18px 0;border-top:1px solid #e2e8f0;color:#4e5968;font-size:14px}
.search-steps li span{min-width:30px;color:#191f28;font-weight:700}
.proof-chapter,.continuity-chapter{background:#eff5ff}
.proof-paper{border-top:2px solid #1557d4}
.proof-equation{padding:30px 0;color:#1557d4;font-size:clamp(32px,4vw,48px)}
.proof-paper article{padding:22px 0;border-top:1px solid #cbdaf0}
.proof-paper h3{margin:0 0 12px;color:#253e60;font-size:17px;line-height:1.6;letter-spacing:-.04em}
.proof-paper p{margin:0 0 10px;color:#4e5968;font-size:14px;line-height:1.85}
.proof-paper p.math-type{color:#1e4c91;font-size:25px}
.proof-paper a,.science-examples a{display:inline-flex;min-height:44px;align-items:center;color:#1557d4;font-size:13px;font-weight:600}
.relation-figure{min-width:0;margin:0}
.relation-figure svg{display:block;width:100%;height:auto;background:#f8fbff}
.relation-fill{fill:#edf4ff}
.relation-outline{fill:none;stroke:#284e82;stroke-width:2}
.relation-join{fill:none;stroke:#1557d4;stroke-width:2;stroke-dasharray:6 4}
.relation-square{fill:none;stroke:#597ba8;stroke-width:1.5}
.relation-points{fill:#1557d4}
.relation-letters{fill:#284e82;font:italic 22px Georgia,serif}
.relation-figure figcaption{display:grid;gap:14px;padding:25px 0;border-top:1px solid #cbdaf0;text-align:center}
.relation-figure figcaption strong{color:#1557d4;font-size:clamp(23px,2.5vw,34px)}
.relation-figure figcaption span{color:#64748b;font-size:12px;line-height:1.6}
.science-examples article{display:grid;grid-template-columns:52px minmax(0,1fr);gap:12px;padding:25px 0;border-top:1px solid #c8d4e5}
.science-symbol{color:#1557d4;font-size:62px;line-height:1}
.science-examples h3{margin:0 0 14px;color:#191f28;font-size:18px;letter-spacing:-.05em}
.science-examples p{margin:0 0 12px;color:#4e5968;font-size:14px;line-height:1.85}
.science-examples p.math-type{color:#1557d4;font-size:clamp(20px,2vw,27px);line-height:1.5;overflow-wrap:anywhere}
.worked-solution{display:grid;grid-template-columns:.85fr 1fr;align-items:center;gap:12px}
.rectangle-example{position:relative;min-width:0}
.rectangle-example svg{display:block;width:100%}
.rectangle-example>span{position:absolute;color:#5077b2;font-size:12px}
.rectangle-width{top:0;left:35%}
.rectangle-height{top:50%;right:0}
.calculation-steps{display:grid;gap:26px;margin:0;padding:0;list-style:none}
.calculation-steps li{display:grid;gap:9px}
.calculation-steps li>span{color:#64748b;font-size:12px}
.calculation-steps strong{color:#1557d4;font-size:clamp(24px,2.5vw,34px)}
.worked-solution>p{grid-column:1/-1;margin:20px 0 0;padding:20px 0 0;border-top:1px solid #e2e8f0;color:#4e5968;font-size:14px;line-height:1.9}
.learning-thread{padding-left:24px;border-left:2px solid #afc8ec}
.learning-thread article{position:relative;padding:20px 0}
.learning-thread article::before{position:absolute;top:22px;left:-31px;width:12px;height:12px;border:3px solid #eef5ff;border-radius:50%;background:#1557d4;content:""}
.learning-thread article>span{color:#1557d4;font-size:12px;font-weight:700}
.learning-thread h3{margin:8px 0 12px;color:#191f28;font-size:18px;letter-spacing:-.05em}
.learning-thread p{margin:0 0 8px;color:#4e5968;font-size:14px;line-height:1.85}
.learning-thread p.math-type{color:#284e82;font-size:25px}
.record-sample{padding:30px;border:1px solid #d8e2f1;background:#fff}
.record-tags{color:#64748b;font-size:12px}
.record-sample h3{margin:13px 0 22px;color:#191f28;font-size:27px;letter-spacing:-.06em}
.record-formula{padding:25px 0;margin:0 0 20px;background:#eff5ff;color:#1557d4;text-align:center;font-size:37px}
.record-sample dl{margin:0}
.record-sample dl>div{padding:16px 0;border-top:1px solid #e2e8f0}
.record-sample dt{margin-bottom:7px;color:#191f28;font-size:13px;font-weight:700}
.record-sample dd{margin:0;color:#4e5968;font-size:13px;line-height:1.8}
.record-sample dd.math-type{font-size:20px}
.revisit-visual{padding:20px 0;border-block:1px solid #d8e2f1}
.bookmark-drawing{display:block;width:64px;height:80px;margin-bottom:24px}
.revisit-visual h3{margin:0 0 22px;color:#191f28;font-size:22px;letter-spacing:-.05em}
.revisit-visual ul{margin:0;padding:0;list-style:none}
.revisit-visual li{display:grid;gap:6px;padding:15px 0;border-top:1px solid #e2e8f0}
.revisit-visual strong{color:#2b466c;font-size:16px;font-weight:600}
.revisit-visual li span{color:#64748b;font-size:13px}
.collection-details h3{margin:0 0 22px;color:#191f28;font-size:24px;letter-spacing:-.05em}
.collection-details details{padding:17px 0;border-top:1px solid #d2dce9}
.collection-details summary{position:relative;min-height:44px;padding:9px 28px 9px 0;color:#191f28;font-size:15px;line-height:1.7;font-weight:600;cursor:pointer}
.collection-details details p{margin:6px 0 5px;color:#4e5968;font-size:14px;line-height:1.85}
.identity-art{overflow:hidden;padding:46px 24px;border-block:1px solid #d5dfef;background:#f2f6fc}
.identity-art img{display:block;width:min(100%,300px);height:auto;margin:0 auto 45px}
.identity-art>div{display:flex;align-items:center;justify-content:space-around;gap:8px;padding-block:30px;border-block:1px solid #d5dfef;color:#537cad;font:50px/1.5 Georgia,serif}
.identity-art>p{margin:30px 0 0;color:#4e5968;font-size:14px;text-align:center}
@media(max-width:980px){
  .long-chapter{gap:36px;padding-block:70px}
  .chapter-copy>p:not(.chapter-caption){font-size:15px}
  .thought-sheet{padding:24px}
  .record-sample{padding:22px}
}
@media(max-width:740px){
  .about-page .launch,.about-page .intro,.about-page .about-notes,.about-page .about-end{min-height:0}
  .long-chapter{min-height:0;grid-template-columns:minmax(0,1fr);gap:35px;padding:64px var(--about-pad)}
  .chapter-copy h2{font-size:clamp(31px,6.5vw,44px);margin-bottom:22px}
  .chapter-caption{margin-bottom:18px;font-size:12px}
  .chapter-copy>p:not(.chapter-caption){line-height:1.9}
  .chapter-nav{justify-content:flex-start;gap:22px}
  .chapter-nav a{font-size:11px}
  .proof-paper p.math-type,.learning-thread p.math-type{font-size:23px}
  .science-examples article{grid-template-columns:40px minmax(0,1fr);gap:8px}
  .science-symbol{font-size:49px}
  .science-examples p.math-type{font-size:clamp(18px,4vw,25px)}
  .worked-solution{grid-template-columns:.8fr 1fr}
  .calculation-steps strong{font-size:clamp(21px,5vw,30px)}
  .identity-art{padding:34px 22px}
}
@media(max-width:560px){
  .about-page .info-header{height:88px;min-height:88px}
  .chapter-nav{top:88px}
  .long-chapter[id],#formula-lab{scroll-margin-top:156px}
  .search-demo input{padding:12px;font-size:16px}
  .search-demo button{min-width:66px;padding-inline:8px}
  .rectangle-height{right:-1px;font-size:10px}
  .record-formula{font-size:32px}
}