:root{color-scheme:light;font-family:PingFang SC,Microsoft YaHei,Helvetica Neue,Roboto,Droid Sans Fallback,WenQuanYi Micro Hei,sans-serif;color:#17213a;background:#f5f7fb;--orange: #ffad3d;--blue: #328cff;--overlap: #6552c8;--ink: #17213a}*{box-sizing:border-box}body{margin:0}button,input{font:inherit}.app{min-height:100vh;display:grid;align-content:start;gap:14px;padding:16px 24px 28px;background:radial-gradient(circle at 14% 0,rgba(255,173,61,.2),transparent 30%),radial-gradient(circle at 88% 2%,rgba(50,140,255,.18),transparent 32%),#f5f7fb}.hero,.lesson-module{width:min(1180px,100%);margin:0 auto;border:1px solid rgba(23,33,58,.1);border-radius:16px;background:#ffffffeb;box-shadow:0 18px 44px #2b3e5d1a}.hero{min-height:96px;display:flex;align-items:center;justify-content:space-between;gap:24px;padding:12px 24px}.eyebrow{margin:0 0 4px;color:#66738d;font-size:.72rem;font-weight:800;letter-spacing:.12em}.hero h1{margin:0;display:flex;align-items:center;gap:14px;font-size:clamp(2.3rem,5vw,3.5rem);line-height:.88}.fraction{min-width:.75em;display:inline-grid;justify-items:center;line-height:.92;vertical-align:middle}.fraction>span:first-child{width:100%;padding:0 .12em .08em;border-bottom:.075em solid currentColor;text-align:center}.fraction>span:last-child{padding-top:.08em}.inputs{display:flex;align-items:center;gap:12px}.input-operator{font-size:1.5rem;font-weight:900}.fraction-input{display:grid;justify-items:center;gap:6px;color:#65728d;font-size:.78rem;font-weight:900}.fraction-input__stack{width:76px;display:grid;gap:5px;padding:8px 10px;border-radius:10px;background:var(--ink)}.fraction-input input{width:100%;min-height:28px;border:0;border-radius:6px;background:#fff;color:var(--ink);font-weight:900;text-align:center}.lesson-module{padding:16px 20px;display:grid;gap:16px}.step-track{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.step-track button{min-height:48px;border:1px solid #dbe2ed;border-radius:12px;background:#f7f9fc;color:#8b96a9;font-weight:800;cursor:pointer}.step-track button span{width:25px;height:25px;margin-right:8px;display:inline-grid;place-items:center;border-radius:50%;background:#dfe5ee}.step-track button.is-active{border-color:#328cff57;background:#edf5ff;color:var(--ink)}.step-track button.is-active span{background:var(--ink);color:#fff}.model-stage{min-height:290px;display:grid;grid-template-columns:minmax(220px,.72fr) minmax(380px,1.28fr);align-items:center;gap:28px;padding:8px 24px 12px}.stage-copy{display:grid;gap:12px;align-content:center}.stage-number{color:#b8c1d0;font-size:3.5rem;font-weight:900;line-height:.85}.stage-copy h2{margin:0;display:flex;flex-wrap:wrap;align-items:center;gap:8px;font-size:clamp(1.35rem,2.5vw,2rem);line-height:1.35}.stage-copy h2 .fraction{font-size:1.2em}.stage-copy p{min-height:42px;margin:0;display:flex;flex-wrap:wrap;align-items:center;gap:7px;color:#65728d;font-size:1rem;font-weight:700;line-height:1.7}.model-card{width:min(720px,100%);min-width:0;justify-self:center}.area-grid{width:100%;aspect-ratio:2 / 1;display:grid;grid-template-columns:repeat(var(--columns),1fr);grid-template-rows:repeat(var(--rows),1fr);overflow:hidden;border:4px solid var(--ink);border-radius:12px;background:#fff}.area-cell{box-shadow:inset -2px -2px #17213a8c;transition:background-color .42s ease,transform .42s ease}.area-cell--first{background:var(--orange)}.area-cell--overlap{background:var(--overlap)}.area-cell--unit-example{box-shadow:inset 0 3px 0 var(--blue),inset 0 -3px 0 var(--blue),inset -2px -2px #17213a8c}.model-card--step-3 .area-cell--unit-example:first-child{border-left:3px solid var(--blue)}.reveal{min-height:76px;display:flex;align-items:center;justify-content:space-between;gap:18px;padding-top:20px;border-top:1px solid #e2e7ef}.visual-legend{display:flex;flex-wrap:wrap;gap:16px;color:#65728d;font-size:.9rem;font-weight:700}.visual-legend span{display:flex;align-items:center;gap:7px}.swatch{width:16px;height:16px;border-radius:4px}.swatch--first{background:var(--orange)}.swatch--overlap{background:var(--overlap)}.next-button{min-height:46px;padding:0 20px;border:0;border-radius:12px;background:var(--ink);color:#fff;font-weight:900;cursor:pointer}.next-button span{margin-left:12px}.result{display:flex;align-items:center;gap:18px}.result__count{color:#65728d;font-weight:800}.result strong{display:flex;align-items:center;gap:12px;padding:12px 18px;border-radius:12px;background:var(--ink);color:#fff;font-size:clamp(1.25rem,3vw,1.8rem)}.result .fraction{font-size:1em}.spotlight-shell{width:min(980px,92vw);margin:0 auto;padding:30px 0;display:grid;gap:16px}.spotlight-shell .hero{width:100%;display:block;min-height:auto}.spotlight-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:16px}.panel{padding:22px;border:1px solid rgba(23,33,58,.1);border-radius:16px;background:#fff;box-shadow:0 14px 32px #2b3e5d14}.panel h2{margin-top:0}.panel ul{margin-bottom:0;padding-left:20px;line-height:1.8;color:#53617a}.subtitle,.panel p{color:#5f6f8c;line-height:1.7}@media (max-width: 840px){.app{padding:14px}.hero{align-items:start;padding:18px}.step-track{grid-template-columns:repeat(2,1fr)}.model-stage,.spotlight-grid{grid-template-columns:1fr}.model-stage{gap:24px;padding:8px}.model-card{width:min(620px,100%);margin:0 auto}.reveal,.result{align-items:stretch;flex-direction:column}.result strong{justify-content:center}}@media (max-width: 560px){.hero{display:grid}.hero h1{font-size:3rem}.inputs{justify-content:space-between}.step-track{grid-template-columns:1fr}.lesson-module{padding:14px}.result strong{gap:8px;font-size:1.15rem}}@media (prefers-reduced-motion: reduce){.area-cell{transition:none}}