:root{--bg:#f3f7f4;--paper:#fffefa;--ink:#29433e;--muted:#5d736b;--green:#36786c;--deep:#205f56;--line:#d6e3dc;--gold:#947025;--serif:'Yu Mincho','Hiragino Mincho ProN','Noto Serif CJK JP',serif;font:16px/1.75 'Yu Gothic','Hiragino Kaku Gothic ProN','Noto Sans CJK JP',sans-serif;color-scheme:light}
*{box-sizing:border-box}body{margin:0;background:radial-gradient(ellipse at 12% 0,#fffbee,transparent 50%),var(--bg);color:var(--ink)}h1,h2,h3,p{margin:0}button,input{font:inherit;color:inherit}button,a,input{touch-action:manipulation;-webkit-tap-highlight-color:transparent}button{cursor:pointer}a{color:inherit;text-decoration:none}button:disabled{cursor:default;opacity:.45}button:focus-visible,a:focus-visible,input:focus-visible,summary:focus-visible{outline:3px solid #ba923c;outline-offset:3px}[hidden]{display:none!important}strong,b{font-weight:600}.shell{width:min(1220px,calc(100% - 36px));margin:auto;padding-bottom:24px}.top-nav{display:flex;justify-content:center;gap:10px;padding:12px 0}.top-nav a{border:1px solid #aec5b8;background:#ffffffca;border-radius:10px;padding:6px 17px;font-size:.875rem;min-height:40px;display:flex;gap:8px;align-items:center}.icon{width:18px;height:18px;fill:none;stroke:currentColor;stroke-width:1.6;stroke-linecap:round;stroke-linejoin:round}.brand{font-size:.8125rem;text-align:center;letter-spacing:.07em;color:var(--muted);margin-bottom:6px}.title{display:flex;justify-content:center;align-items:center;gap:12px;flex-wrap:wrap}.title h1{font:500 clamp(1.3rem,2.4vw,1.9rem)/1.5 var(--serif)}.number{color:#6b9786;font:2rem/1 Georgia,serif}.level{border:1px solid #deceac;background:#fff9e9;color:#806127;border-radius:20px;font-size:.875rem;padding:1px 10px}.question-nav{display:flex;gap:6px;justify-content:center;flex-wrap:wrap;margin:12px auto 16px}.question-nav a{border:1px solid var(--line);border-radius:8px;width:37px;min-height:34px;display:grid;place-items:center;background:#ffffffbb;font-size:.875rem;position:relative}.question-nav a[aria-current=page]{color:white;background:var(--green);border-color:var(--green)}.question-nav a.done:after{content:'✓';position:absolute;top:-8px;right:-4px;background:#faf2d7;color:#7f6528;font-size:.75rem;border-radius:50%;width:16px;height:18px;line-height:18px;text-align:center}.layout{display:grid;grid-template-columns:minmax(0,1.45fr) minmax(350px,1fr);gap:15px;align-items:start}.panel{min-width:0;background:var(--paper);border:1px solid var(--line);border-radius:18px;box-shadow:0 8px 28px #244d3c08}.problem-panel{grid-column:2;grid-row:1;padding:19px 22px}.eyebrow{font-size:.875rem;letter-spacing:.1em;color:var(--green);margin-bottom:8px}.problem{font-size:1rem;line-height:1.95}.ask{border-left:3px solid #97b6a1;padding-left:12px;margin-top:12px;line-height:1.85;font-weight:600}.model-panel{grid-column:1;grid-row:1/span 2;padding:16px;position:sticky;top:12px}.model-heading{display:flex;justify-content:space-between;align-items:center;gap:8px;margin-bottom:10px}.model-heading h2{font-size:1rem;font-weight:500}.reset{border:0;background:none;padding:7px 4px;color:var(--muted);font-size:.875rem}.instruction{font-size:.9375rem;line-height:1.7;margin-bottom:10px}.stage{border:1px solid #d5e3da;background:linear-gradient(155deg,#fcfefb,#edf5ef);border-radius:13px;overflow:hidden}.chart-head{padding:10px 13px 0;font-size:.875rem;color:var(--muted);display:flex;justify-content:space-between;gap:12px}.chart-head b{color:var(--deep);font-weight:500}.diagram{width:100%;height:auto;display:block}.diagram text{font-family:'Yu Gothic','Noto Sans CJK JP',sans-serif;fill:var(--ink);font-size:23px}.diagram .muted{fill:var(--muted);font-size:20px}.diagram .small{font-size:19px}.diagram .value{font-size:25px;font-weight:600}.diagram .positive{fill:#276b61}.diagram .negative{fill:#956b20}.chart-note{border-top:1px solid #dce6df;padding:7px 12px;font-size:.875rem;color:var(--muted);line-height:1.6;background:#ffffff90}.legend{display:flex;gap:7px;flex-wrap:wrap;padding:9px 11px}.legend-item{flex:1;min-width:76px;border-left:3px solid var(--c);padding-left:7px;font-size:.875rem;line-height:1.6}.legend-item span,.legend-item b{display:block}.legend-item b{font-weight:500}.legend-item small{font-size:.8125rem;color:var(--muted)}.controls{display:flex;flex-wrap:wrap;align-items:center;gap:8px;margin-top:11px}.btn{border:1px solid #b2cabb;border-radius:9px;padding:7px 12px;min-height:42px;background:white;font-size:.875rem;line-height:1.6;display:inline-flex;align-items:center;justify-content:center;gap:6px}.btn:hover:not(:disabled){background:#eef6f0}.btn.primary{background:var(--green);border-color:var(--green);color:white}.btn.primary:hover:not(:disabled){background:var(--deep)}.btn.gold{background:#fff7e1;border-color:#dcca9f;color:#866324}.btn[aria-pressed=true]{background:#e6f1e9;border-color:#659a7e;color:var(--deep)}.slider-wrap{width:100%;padding:8px 10px;background:#eff5ef;border-radius:10px}.slider-label{display:flex;justify-content:space-between;gap:12px;font-size:.9375rem}.slider-label output{color:var(--deep);font-weight:600;white-space:nowrap}.slider-row{display:flex;align-items:center;gap:13px;margin-top:4px}.slider-row .btn{padding:0;width:38px;min-height:38px;font-size:1.3rem;flex-shrink:0}input[type=range]{width:100%;min-width:0;accent-color:var(--green);min-height:40px;cursor:pointer}.readout{display:flex;gap:10px;justify-content:space-between;align-items:center;padding:9px 12px;margin-top:10px;border-radius:10px;background:#eef4ed;font-size:.9375rem;line-height:1.65;min-height:46px}.readout.good{background:#e6f1e6}.readout strong{color:var(--deep)}.area-key{display:flex;gap:16px;flex-wrap:wrap;font-size:.875rem;margin:9px 0 0;color:var(--muted)}.swatch{display:inline-block;width:13px;height:13px;border-radius:3px;margin-right:5px;border:1px solid;vertical-align:-1px}.swatch.up{background:#84baa47a;border-color:#43866d}.swatch.down{background:#e2c07688;border-color:#bc9138}.work-panel{grid-column:2;grid-row:2;padding:18px 22px}.answer-label{font-size:1rem;font-weight:500;margin-bottom:10px}.answer-item{display:flex;justify-content:space-between;align-items:center;gap:10px;margin:8px 0}.answer-item label{font-size:.9375rem;line-height:1.65}.answer-box{display:flex;gap:7px;align-items:center;flex-shrink:0;font-size:.9375rem}.answer-box input{width:94px;min-height:43px;text-align:center;font-size:1.3rem;background:white;border:1px solid #a4c1b0;border-radius:8px}.answer-box input[aria-invalid=true]{border-color:#b88731;background:#fff8e7}.answer-check{width:100%;margin-top:7px}.feedback{font-size:.9375rem;line-height:1.7;color:#866324;margin-top:9px}.feedback:empty{display:none}.feedback.good{color:var(--deep)}.support{border-top:1px solid var(--line);padding-top:12px;margin-top:14px}.hint-top{display:flex;justify-content:space-between;align-items:center;gap:8px}.hint-counter{font-size:.875rem;color:var(--muted)}.hint{background:#fff8e6;border:1px solid #e1d3af;border-radius:9px;padding:10px 12px;font-size:.9375rem;line-height:1.8;margin-top:9px}.hint p+p{border-top:1px solid #e3d8bd;padding-top:7px;margin-top:7px}.reward{display:flex;align-items:center;gap:11px;margin:11px 0;padding:10px 12px;background:#f6edce50;border:1px solid #ddcda6;border-radius:11px}.medal{width:48px;height:48px;flex-shrink:0;border:3px double #b69953;background:#e7c77235;border-radius:50%;color:#98762e;font:1.45rem Georgia,serif;opacity:.8;display:grid;place-items:center}.reward b{font-weight:500;color:#7c6228}.reward p{font-size:.875rem;color:var(--muted)}.notebook{border:1px solid #bbd0c0;border-radius:11px;background:#fbfcf7;margin-top:15px}.notebook>summary,.solution>summary{cursor:pointer;padding:10px 12px;font-size:.9375rem;color:var(--deep)}.nb-body{padding:0 12px 14px}.nb-intro{font-size:.875rem;color:var(--muted);line-height:1.7;border-top:1px solid var(--line);padding-top:8px}.step{border-top:1px solid #dce5dc;padding-top:13px;margin-top:13px}.step h3{font-size:1rem;font-weight:500;line-height:1.7}.step .why{font-size:.875rem;color:var(--muted);line-height:1.7;margin:6px 0}.expr-row{display:flex;gap:6px;align-items:center}.expr-row input{width:100%;min-width:0;border:1px solid #adc6b7;border-radius:7px;font-size:1.05rem;padding:7px 9px;min-height:42px;background:#fff}.expr-row input::placeholder{font-size:.875rem}.expr-row .btn{padding:6px 9px;flex-shrink:0}.expr-example{margin-top:8px;border:0;background:none;color:#6c7958;text-decoration:underline;text-underline-offset:4px;font-size:.875rem;padding:3px 0}.expr-result{font-size:.875rem;margin-top:7px;color:#806128;line-height:1.7}.expr-result.good{color:var(--deep)}.example{margin-top:8px;padding:8px 10px;background:#f8f1dd;border-radius:7px;font-size:1.125rem;overflow-wrap:anywhere}.solution{border-top:1px solid var(--line);margin-top:14px;font-size:.9375rem}.solution>summary{padding:10px 0}.solution ol{padding-left:23px;margin:4px 0 12px}.solution li{margin-top:9px}.solution .formula{display:block;font-size:1.125rem;overflow-wrap:anywhere;color:var(--deep)}.takeaway{border-left:3px solid #b6a264;background:#f7f1df;padding:9px 11px;margin:12px 0;line-height:1.85}.answer-final{padding:10px 12px;background:#eaf3ec;border-radius:9px;font-size:1rem}.answer-final span{display:block}.next-row{display:flex;justify-content:space-between;gap:12px;margin-top:17px;padding-top:12px;border-top:1px solid var(--line);font-size:.875rem}.footer{text-align:center;font-size:.8125rem;color:var(--muted);margin:18px 0 0}.skip-link{position:absolute;left:16px;top:-100px;padding:10px;background:white;z-index:5}.skip-link:focus{top:10px}
.block-board{padding:16px 14px 7px}.pile-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:10px}.pile{background:#ffffff88;border:1px solid #ccddd1;border-radius:10px;padding:8px 5px;min-width:0;display:flex;flex-direction:column;align-items:center;gap:4px}.pile[aria-pressed=true]{border-color:#ac8330;box-shadow:0 0 0 3px #e0c48770;background:#fff9e8}.pile .person{font-size:.9375rem}.stack{height:240px;width:100%;display:flex;flex-direction:column-reverse;gap:3px;align-items:center;justify-content:flex-start;padding-bottom:4px;position:relative}.block{display:block;width:78%;height:var(--block-h);border-radius:3px;flex-shrink:0;background:linear-gradient(150deg,#a5cbb6,#669987);border:1px solid #588c77;box-shadow:inset 1px 2px 0 #e4f0df7a,1px 2px 0 #39665020}.pile:nth-child(even) .block{background:linear-gradient(150deg,#b6cfdc,#7c9fb0);border-color:#648b9d}.pile .count{font-size:1.2rem;font-weight:500}.pile .count small{font-size:.875rem}.empty-stack{font-size:.875rem;color:var(--muted);position:absolute;bottom:20px}.block-total{text-align:center;padding:9px 0 4px;font-size:.9375rem}.waiting{padding:65px 24px;text-align:center;min-height:260px;display:flex;flex-direction:column;justify-content:center;gap:16px}.waiting strong{font-size:1.25rem;font-weight:500}.correction-story{font-size:1.1rem;display:flex;gap:15px;justify-content:center;align-items:center}.condition-tabs{display:flex;gap:7px;width:100%}.condition-tabs .btn{flex:1}.toc-header{text-align:center;padding:14px 0 24px}.toc-header h1{font:500 2.25rem/1.5 var(--serif);letter-spacing:.12em}.toc-header p{color:var(--muted);font-size:1rem;margin-top:8px}.toc-section{margin:14px 0 24px}.toc-section>h2{font:500 1.2rem var(--serif);border-bottom:1px solid #bed1c3;padding-bottom:10px;margin-bottom:12px;display:flex;justify-content:space-between}.toc-section>h2 span{font: .875rem 'Yu Gothic',sans-serif;color:var(--muted)}.toc-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px}.toc-card{background:var(--paper);border:1px solid var(--line);border-radius:14px;padding:16px;display:grid;grid-template-columns:76px minmax(0,1fr) 14px;gap:13px;align-items:center;box-shadow:0 5px 18px #37503906;min-height:128px}.toc-card:hover{border-color:#8eb49d;background:#fffffc}.toc-card h3{font:500 1.12rem/1.7 var(--serif);margin-top:3px}.toc-card p{font-size:.875rem;color:var(--muted);line-height:1.7;margin-top:3px}.toc-meta{font-size:.875rem;color:var(--muted)}.toc-meta b{font:1.4rem Georgia,serif;color:#739783;margin-right:10px}.toc-card svg{width:76px;height:72px}.toc-notes{padding:13px 16px;border-left:3px solid #a3baa0;font-size:.9375rem;color:var(--muted)}
@media(max-width:850px){.shell{width:min(700px,calc(100% - 24px))}.layout{display:flex;flex-direction:column;gap:12px}.panel{width:100%}.problem-panel{order:0;padding:15px 18px}.model-panel{order:1;position:static;padding:13px}.work-panel{order:2;padding:16px 18px}.title h1{font-size:1.45rem}.question-nav{max-width:400px;gap:7px}.question-nav a{width:42px;min-height:35px}.brand{letter-spacing:.01em}.toc-grid{grid-template-columns:1fr}.stack{height:200px}.chart-head{font-size:.875rem}}
@media(max-width:480px){.shell{width:calc(100% - 18px)}.top-nav{padding:9px 0}.top-nav a{padding:5px 13px}.title{gap:7px}.title h1{font-size:1.25rem}.number{font-size:1.7rem}.level{padding:1px 8px;font-size:.8125rem}.question-nav{gap:6px;max-width:335px;margin:10px auto 13px}.question-nav a{width:38px;min-height:34px}.brand{font-size:.75rem}.problem-panel{padding:13px 15px}.problem,.ask{font-size:1rem;line-height:1.85}.eyebrow{margin-bottom:5px}.model-panel{padding:11px}.model-heading h2{font-size:.9375rem}.instruction{font-size:.9375rem}.diagram text{font-size:27px}.diagram .value{font-size:28px}.diagram .small,.diagram .muted{font-size:25px}.chart-head{display:block;padding:8px 10px 0}.chart-head span{display:block}.chart-note{font-size:.875rem}.legend{gap:7px;padding:8px}.legend-item{min-width:67px;font-size:.875rem}.legend-item small{font-size:.8125rem}.work-panel{padding:14px 15px}.answer-item{flex-wrap:wrap;gap:6px}.answer-box{margin-left:auto}.answer-box input{width:87px}.readout{font-size:.875rem;align-items:flex-start;flex-direction:column;gap:2px}.controls{gap:7px}.btn{min-height:42px}.pile-grid{gap:6px}.block-board{padding:12px 8px 5px}.pile{padding:7px 3px}.stack{height:180px}.pile .person{font-size:.875rem}.waiting{padding:35px 16px;min-height:220px}.toc-card{grid-template-columns:60px minmax(0,1fr) 12px;padding:13px;gap:10px}.toc-card svg{width:60px}.toc-header{padding:8px 0 20px}.toc-header h1{font-size:2rem}.toc-card h3{font-size:1.06rem}.toc-card p{font-size:.875rem}.toc-section>h2{font-size:1.12rem}}
@media(prefers-reduced-motion:no-preference){.btn,a{transition:background .15s,border-color .15s}.reward{animation:appear .35s ease-out}@keyframes appear{from{opacity:0;transform:translateY(5px)}to{opacity:1;transform:translateY(0)}}}
@media print{.top-nav,.question-nav,.controls,.answer-check,.support,.notebook,.next-row,.reset,.skip-link{display:none}.shell{width:100%}.model-panel{position:static}.layout{display:block}.panel{box-shadow:none;margin:12px 0;break-inside:avoid}.solution{display:block}.footer{margin-top:12px}}

/* Direct manipulation and a short path from the figure to arithmetic. */
.work-trail{display:flex;list-style:none;gap:6px;padding:0;margin:0 0 12px;font-size:.875rem}.work-trail li{flex:1;text-align:center;border-bottom:2px solid #dfe7df;padding:4px 2px;color:#738176}.work-trail .current{border-color:#b79849;color:#83642b;background:#fff9e9}.work-trail .done{border-color:#66987a;color:#35705a}.instruction{background:#f2f6ed;border-left:3px solid #b7c898;padding:9px 12px;border-radius:0 9px 9px 0;line-height:1.8}.diagram{max-height:295px}.diagram-grip{cursor:ns-resize;touch-action:none;outline:none}.diagram-grip[data-gesture=width]{cursor:ew-resize}.diagram-grip:hover>rect:not(.grip-hit-area),.diagram-grip:focus-visible>rect:not(.grip-hit-area){fill:#f6e7b8;stroke:#795917;stroke-width:3}.diagram-group{transition:opacity .2s}.area-dimensions{display:flex;justify-content:center;gap:10px;flex-wrap:wrap;padding:10px;font-size:.9375rem}.area-dimensions b{display:block;text-align:center;color:var(--deep);font-size:1.13rem;font-weight:500}.area-dimensions span{flex:1;text-align:center;border-right:1px solid #d5e2d5}.area-dimensions span:last-child{border:0}.fine-controls{font-size:.875rem;width:100%;color:var(--muted)}.fine-controls summary{cursor:pointer;padding:3px 0;text-decoration:underline;text-underline-offset:3px}.fine-controls .slider-wrap{margin-top:6px}.direct-readout{display:flex;align-items:center;justify-content:space-between;gap:14px;width:100%;padding:7px 12px;background:#f1f5ef;border-radius:9px;font-size:.9375rem}.direct-readout output{font-size:1.4rem;color:var(--deep);font-weight:500}.model-panel .controls{gap:7px;margin-top:8px}.model-panel .area-key{margin-top:8px}.manip-tray{display:flex;gap:14px;align-items:center;margin-top:11px;border:1px solid #cfddd0;border-radius:12px;background:#fbfcf7;padding:10px 13px}.manip-tray p{font-size:.9375rem;line-height:1.75}.manip-tray small{display:block;font-size:.8125rem;color:var(--muted)}.draggable-card{position:relative;touch-action:none;user-select:none;cursor:grab;background:linear-gradient(135deg,#f2f8ed,#dcebdd);border:1.5px solid #8eb29a;box-shadow:0 4px 0 #71988028;border-radius:10px;padding:9px 14px;min-width:120px;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:0;min-height:75px;flex-shrink:0;font-size:.875rem}.draggable-card b{font-size:1.4rem;line-height:1.5;font-weight:500;color:#32634f}.draggable-card:active{cursor:grabbing}.draggable-card:disabled{opacity:.5;cursor:default;box-shadow:none}.card-grip{position:absolute;left:6px;top:4px;font-size:1.05rem;color:#6f8f79;line-height:1}.points-card{background:linear-gradient(135deg,#fff9e6,#f1e3ba);border-color:#c6ad64}.points-card b{color:#846322}.block{position:relative;touch-action:none;cursor:grab;user-select:none}.block-grip{position:absolute;inset:0;display:grid;place-items:center;color:#3c674f;font-size:20px;line-height:8px;overflow:hidden}.block:hover{filter:brightness(1.07);outline:2px solid #bca566;outline-offset:1px}.pile.drop-ready,.stage.drop-ready,.person-target.drop-ready{background:#e6f3d8;outline:3px solid #b19843;outline-offset:-3px}.drag-source{opacity:.5}.drag-ghost{position:fixed;z-index:1000;pointer-events:none;transform:translate(-50%,-65%) rotate(-3deg);padding:12px 18px;border:1.5px solid #b19843;background:#fff7d9ed;color:#66501f;box-shadow:0 9px 25px #30402b25;border-radius:9px;font-size:1rem;white-space:nowrap}.block-ghost{background:linear-gradient(150deg,#b9d6b7,#82ac91);color:#264f37;border-color:#719479;padding:7px 19px}.is-dragging,.is-dragging *{user-select:none!important;cursor:grabbing!important}.swap-tray{display:grid;grid-template-columns:1fr 36px 1fr;gap:11px;align-items:center;margin-top:12px}.swap-tray .draggable-card,.person-target{min-width:0;width:100%;padding:10px;min-height:111px}.person-target{border:2px dashed #91aebc;border-radius:12px;background:#f1f7fa;display:flex;flex-direction:column;gap:1px;align-items:center;justify-content:center;font-size:.875rem;color:#497184}.person-target b,.person-card b{font-size:1rem;font-weight:500}.person-symbol{height:36px;line-height:1}.person-target .person-symbol{color:#628ea3}.person-card .person-symbol{color:#538972}.exchange-mark{text-align:center;font-size:1.65rem;color:#a48b47}.swap-receipt{border:1px solid #c5d6c7;background:#eef5e9;padding:9px 12px;border-radius:9px;margin-top:10px;font-size:.9375rem}.readout{display:block;margin-top:10px}.readout>span,.readout>strong{display:block}.readout>strong{font-weight:500;margin:4px 0}.readout>p{font-size:.875rem;line-height:1.7;margin-top:5px;text-align:center}.balance-pair{display:grid;grid-template-columns:minmax(0,1fr) 26px minmax(0,1fr);gap:7px;align-items:center}.balance-pair>div{padding:6px 8px;border-radius:8px;text-align:center;line-height:1.6}.balance-pair span{font-size:.875rem}.balance-pair b{font-size:1.35rem;display:block;font-weight:500}.balance-pair small{font-size:.875rem;margin-left:4px}.balance-up{background:#e0eee0;color:#31664d}.balance-down{background:#f5e9c7;color:#806127}.balance-equals{font-size:1.3rem!important;text-align:center;color:#728065}.next-learning{border-top:1px solid #d9e2d4;margin-top:12px;padding-top:11px;font-size:.9375rem;line-height:1.8}.next-learning .btn{width:100%;margin-top:8px}.figure-to-formula{margin-top:10px;border:1px solid #dbcc9e;background:#fbf5df;padding:10px 12px;border-radius:10px;font-size:.9375rem;line-height:1.75}.figure-to-formula span{font-size:.8125rem;color:#8f753b;display:block}.figure-to-formula strong{font-weight:500;display:block;margin:3px 0}.figure-to-formula p{color:#617653;font-size:.875rem}.work-panel .notebook{margin:0 0 16px}.work-panel .notebook>summary{line-height:1.8}.step{border:0;margin-top:8px;padding-top:4px}.step-count{font-size:.8125rem;color:#8a7337;margin:5px 0}.step h3{font-size:1.1rem;font-weight:500}.word-formula{border-left:3px solid #8fa87a;background:#edf3e7;padding:10px 11px;margin:12px 0;font-size:1rem;line-height:1.8;overflow-wrap:anywhere}.nb-navigation{display:flex;justify-content:space-between;gap:8px;margin-top:14px}.nb-intro{font-size:.875rem}.expr-row{flex-wrap:wrap}.expr-row input{flex:1 1 170px}.expr-row .btn{min-width:54px}.expr-row input::placeholder{font-size:.8125rem}.answer-label{border-top:1px solid #dce5d9;padding-top:10px}.reward{padding:10px 13px;gap:13px;min-height:127px;background:linear-gradient(120deg,#faf1d866,#eef4e73d);border:1px solid #d8c894;overflow:visible}.reward .medal-wrap{position:relative;flex:0 0 95px;display:grid;place-items:center}.gold-medal{width:95px;height:109px;display:block;opacity:.8}.award-label{font-size:.8125rem!important;letter-spacing:.1em;color:#97772c!important}.reward b{font:500 1.6rem/1.6 var(--serif);color:#8e6b24}.reward p{font-size:.875rem;line-height:1.7}.award-spark{position:absolute;width:5px;height:5px;background:#ceaf57;border-radius:50%;opacity:0;left:47px;top:48px;pointer-events:none}
@media(prefers-reduced-motion:no-preference){.reward-celebrate .gold-medal{animation:award-arrive .85s cubic-bezier(.2,.8,.25,1)}.reward-celebrate .award-spark{animation:award-spark 1.15s ease-out;animation-delay:calc(var(--i)*25ms)}.drop-pulse .stage{animation:drop-confirm .5s ease-out}@keyframes award-arrive{0%{transform:scale(.4) rotate(-15deg);opacity:0}60%{transform:scale(1.13) rotate(4deg);opacity:.85}100%{transform:scale(1) rotate(0);opacity:.8}}@keyframes award-spark{0%{transform:rotate(calc(var(--i)*45deg)) translateY(-23px) scale(.3);opacity:0}30%{opacity:.75}100%{transform:rotate(calc(var(--i)*45deg)) translateY(-74px) scale(.4);opacity:0}}@keyframes drop-confirm{0%{box-shadow:inset 0 0 0 4px #a9bc7177}100%{box-shadow:inset 0 0 0 0 #a9bc7100}}}
@media(max-width:850px){.model-panel{position:static}.diagram{max-height:305px}.nb-intro{font-size:.875rem}.nb-intro::after{content:'（スマートフォンでは上の図）';display:block;font-size:.8125rem;color:#708267}}
@media(max-width:480px){.work-trail{margin-bottom:9px;font-size:.8125rem}.work-trail li{padding:3px 0}.instruction{font-size:.9375rem;padding:8px 10px}.diagram{max-height:240px}.manip-tray{padding:9px;gap:10px}.draggable-card{min-width:105px;padding:9px 12px;min-height:72px}.draggable-card b{font-size:1.25rem}.manip-tray p{font-size:.875rem}.manip-tray small{font-size:.8125rem}.direct-readout{font-size:.9375rem;padding:6px 10px}.direct-readout output{font-size:1.25rem}.model-heading h2{font-size:.9375rem}.reset{font-size:.8125rem}.model-heading{align-items:flex-start}.balance-pair{gap:5px;grid-template-columns:minmax(0,1fr) 20px minmax(0,1fr)}.balance-pair span{font-size:.8125rem}.balance-pair b{font-size:1.2rem}.next-learning{font-size:.9375rem}.gold-medal{width:83px;height:96px}.reward .medal-wrap{flex-basis:83px}.reward{min-height:111px;padding:9px 11px}.reward b{font-size:1.5rem}.reward p{font-size:.875rem}.award-spark{left:41px;top:42px}.area-dimensions{gap:5px;font-size:.8125rem;padding:8px 5px}.area-dimensions b{font-size:1rem}.swap-tray{gap:7px;grid-template-columns:1fr 25px 1fr}.person-target,.swap-tray .draggable-card{min-height:107px}.nb-navigation .btn{font-size:.875rem}.step h3{font-size:1.05rem}}
@media print{.manip-tray,.swap-tray,.work-trail,.fine-controls,.diagram-grip,.next-learning{display:none!important}}

/* Keep the working figure and arithmetic close together. */
.layout{grid-template-rows:min-content 1fr}
.area-math{display:flex;flex-wrap:wrap;align-items:center;justify-content:center;gap:0 4px;font-size:.875rem;line-height:1.65;margin:5px 0 2px;min-height:24px;font-variant-numeric:tabular-nums}
.area-math>span{white-space:nowrap}.area-math .math-plus{opacity:.7}
.balance-pair>div{align-self:stretch;display:flex;flex-direction:column;justify-content:space-between}
.balance-pair b{padding-top:2px;margin-top:2px}
.nb-figure{display:none}.nb-figure-label{display:flex;justify-content:space-between;gap:10px;font-size:.875rem;color:var(--deep);padding:8px 10px 0}
.nb-figure-label span{font-size:.8125rem;color:var(--muted)}
.nb-figure .stage{border:0;background:none;overflow:visible}.nb-figure .chart-head,.nb-figure .chart-note,.nb-figure .legend-item small{display:none}
.nb-figure .diagram{max-height:230px}.nb-figure .legend{padding:4px 10px 10px}.nb-figure .legend-item{font-size:.875rem;min-width:62px}
.nb-block-counts{display:grid;grid-template-columns:repeat(4,1fr);gap:5px;padding:10px;font-size:.875rem;text-align:center}.nb-block-counts b{display:block;font-size:1.1rem;color:var(--deep);background:#deedde;padding:5px 0;border-radius:5px;margin-top:4px}
.nb-figure-note{font-size:.875rem;line-height:1.75;padding:8px 10px;text-align:center}
@media(min-width:851px){.diagram{max-height:260px}.stack{height:205px}.model-panel{padding:14px}.work-panel{padding-top:16px}}
@media(max-width:850px){.nb-figure{display:block;background:#f1f6ee;border:1px solid #d3e0cd;border-radius:10px;margin:12px 0}.nb-figure:empty{display:none}.nb-intro::after{content:none}.nb-body{padding-left:10px;padding-right:10px}}
@media(max-width:480px){.area-math{font-size:.875rem;gap:0 2px}.balance-pair>div{padding:6px}.nb-figure .diagram{max-height:215px}.nb-figure .legend{gap:6px}.nb-figure .legend-item{min-width:64px}.nb-figure .diagram .small{font-size:27px}}
@media print{.nb-figure{display:none!important}}

.practice-return{text-align:center;margin:8px 0 16px;font-size:14px}.practice-return a{display:inline-block;padding:9px 15px;border:1px solid #aec8bb;border-radius:9px;background:#fffefa;color:#286456}.top-nav a{min-height:44px}