:root{--ink:#173836;--paper:#f6f7f2;--lime:#dfff75;--muted:#596967}*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:95px}body{margin:0;background:var(--paper);color:var(--ink);font-family:"Microsoft YaHei","PingFang SC",sans-serif;font-size:16px;line-height:1.8}a{color:inherit}header{max-width:1320px;margin:auto;min-height:100px;padding:22px 48px;display:flex;align-items:center;justify-content:space-between;gap:20px}.brand{text-decoration:none;font-weight:800;font-size:21px}.brand span{display:block;font-size:12px;letter-spacing:3px;font-weight:400}nav{display:flex;gap:30px}nav a{text-decoration:none;font-size:14px}.edition{font-size:12px;border:1px solid #a9b8ac;padding:5px 13px;border-radius:30px}.hero{max-width:1320px;margin:auto;display:grid;grid-template-columns:1.05fr 1fr;gap:50px;padding:48px 48px 80px}.eyebrow{text-transform:uppercase;letter-spacing:2px;font-size:13px;font-weight:600}h1{font-size:clamp(42px,4.5vw,66px);letter-spacing:-2px;line-height:1.3;margin:30px 0}h2{font-size:clamp(28px,3vw,40px);line-height:1.5;letter-spacing:-1px;margin:18px 0}h3{font-size:22px;line-height:1.5;margin:0 0 12px}p{margin:0 0 18px}.intro{color:var(--muted);font-size:18px;max-width:520px}.read{display:inline-flex;gap:46px;align-items:center;text-decoration:none;border-bottom:1px solid var(--ink);padding:18px 0 10px;font-weight:600}.read span{font-size:25px}.meta{display:flex;flex-wrap:wrap;gap:16px;font-size:12px;color:var(--muted);margin-top:42px}.board{background:var(--ink);border-radius:4px;padding:30px 34px;color:#fff;transform:rotate(1deg);position:relative;box-shadow:12px 14px 0 #e1e7db}.board-label{font-size:13px;color:#b3cdc6;letter-spacing:2px}.quote{border-top:1px solid #52736c;padding:18px 0 8px}.q1{margin-top:20px}.quote small{font-size:12px;color:#b8cdc7}.quote p{font-size:25px;line-height:1.55;margin:6px 0 10px}.q2 p{color:var(--lime);font-weight:600}.q3{margin-left:60px}.board-foot{font-size:12px;color:#b8cdc7;text-align:right;letter-spacing:4px}.section{max-width:1224px;margin:auto;padding:80px 48px;border-top:1px solid #c8d0c7}.section-heading{max-width:700px}.section-heading p{color:var(--muted)}#story{display:grid;grid-template-columns:.85fr 1.15fr;gap:75px}.timeline article{display:flex;gap:24px;padding:0 0 35px;margin-bottom:30px;border-bottom:1px solid #d5ddd2}.timeline article:last-child{margin-bottom:0}.number{font-family:Georgia,serif;font-size:32px;color:#84997b;line-height:1.1}.timeline p,.plan p{color:var(--muted)}.note{padding:12px 16px;border-left:3px solid #8baf57;background:#eaf0e3;font-size:14px}.math-section{background:var(--ink);color:#f6f7f2;padding:65px max(48px,calc((100vw - 1128px)/2));}.math-section>.eyebrow{color:var(--lime)}.math-grid{display:grid;grid-template-columns:1fr 1fr;gap:80px;margin-top:34px}.math-grid p{color:#c4d5cc}.rule{display:flex;justify-content:space-between;border-bottom:1px solid #45605b;padding:12px 0}.rule strong{color:var(--lime)}.math-grid small{display:block;font-size:13px;color:#b7ccc5;margin-top:15px}.axis-panel{align-self:center;border:1px solid #537069;padding:26px}.axis-panel svg{display:block;width:100%;height:auto}.axis-panel p{font-size:14px;margin:12px 0 0}.finding-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:36px;margin-top:35px}.finding-grid article{border-top:3px solid var(--ink);padding-top:18px}.finding-grid article>span{font-size:13px;color:var(--muted)}.finding-grid h3{font-size:28px;margin-top:12px}.finding-grid p{color:var(--muted)}.evidence{border:1px solid #bcc9b8;padding:18px 24px;margin-top:25px;font-size:14px;color:var(--muted)}.next{display:grid;grid-template-columns:1fr 1fr;gap:30px 65px}.plan article{display:flex;gap:24px;padding:0 0 20px}.plan article>span{width:34px;height:34px;flex-shrink:0;text-align:center;border-radius:50%;background:#dfebd0}.plan h3{font-size:20px}details{grid-column:1/-1;border-top:1px solid #bdcdb7;border-bottom:1px solid #bdcdb7;padding:20px 0}summary{cursor:pointer;font-weight:600;list-style:none;display:flex;justify-content:space-between}summary::-webkit-details-marker{display:none}summary span{margin-right:10px}details[open] summary span{transform:rotate(45deg)}li{margin-bottom:10px}ul{padding-left:24px}.ending{text-align:center;background:#e4edda;padding:70px 24px}.ending h2{font-size:clamp(30px,3.6vw,46px)}.ending h2 span{font-weight:400}.ending a{display:inline-block;background:var(--ink);color:white;text-decoration:none;padding:14px 30px;margin:12px}.ending p{font-size:12px;color:var(--muted)}footer{padding:34px 48px;max-width:1320px;margin:auto;display:flex;align-items:center;gap:24px;flex-wrap:wrap}footer span{font-size:14px}footer small{font-size:12px;color:var(--muted);margin-left:auto}.skip{position:absolute;left:20px;top:-100px;padding:10px;background:white;z-index:2}.skip:focus{top:10px}a:focus-visible,summary:focus-visible{outline:3px solid #71862d;outline-offset:5px}@media(max-width:800px){header{padding:20px 24px;min-height:85px}nav{display:none}.brand{font-size:18px}.edition{font-size:12px;white-space:nowrap}.hero{padding:28px 24px 60px;grid-template-columns:1fr;gap:38px}h1{margin:23px 0;font-size:44px}.intro{font-size:17px}.meta{margin-top:27px;gap:12px}.board{margin:0 7px 0 0;padding:25px}.quote p{font-size:23px}.q3{margin-left:25px}.section{padding:50px 24px}#story,.next{grid-template-columns:1fr;gap:28px}.timeline article{gap:18px;padding-bottom:25px}.math-section{padding:45px 24px}.math-grid{grid-template-columns:1fr;gap:30px}.finding-grid{grid-template-columns:1fr;gap:18px}.finding-grid h3{font-size:25px}.evidence{padding:16px}.ending{padding:50px 24px}footer{padding:28px 24px;gap:8px;display:grid}footer small{margin-left:0}}@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}}@media print{header nav,.read,.ending a{display:none}.hero,#story,.math-grid,.next{display:block}.board{transform:none;box-shadow:none}body{background:white}.section{padding:25px}article{break-inside:avoid}details ul{display:block}.math-section{background:#fff;color:#173836}.math-section p{color:#173836}}

/* V1.1: teacher practice and factual classroom photography */
.hero-copy,.board,.practice-steps article,.photo-grid figure{min-width:0}.hero h1{font-size:clamp(36px,3.8vw,56px)}.practice-steps{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:28px;margin-top:30px}.practice-steps article{border-top:2px solid #173836;padding-top:18px}.practice-steps article>span{font-size:13px;color:#596967}.practice-steps h3{font-size:20px;margin-top:12px}.practice-steps p{color:#596967}.photo-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:28px;margin-top:30px}.photo-grid figure{margin:0}.photo-grid img{display:block;width:100%;height:auto;border-radius:3px}.photo-grid figcaption{padding:18px 0;border-bottom:1px solid #c8d0c7}.photo-grid figcaption strong{display:block;font-size:18px;margin-bottom:7px}.photo-grid figcaption span{font-size:14px;color:#596967;display:block}.ending .closing-copy{max-width:740px;margin:20px auto;font-size:17px;text-align:left}nav{gap:22px}@media(max-width:1000px){.practice-steps{grid-template-columns:repeat(2,minmax(0,1fr))}}@media(max-width:600px){.practice-steps,.photo-grid{grid-template-columns:minmax(0,1fr)}.hero h1{font-size:36px;letter-spacing:-1px}.photo-grid{gap:24px}}
