.md-board{padding:12px;border:3px solid var(--ink);border-radius:20px;background:#fff7df;margin:10px 0 16px}.md-cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(130px,1fr));gap:12px;align-items:start}.md-observe{display:flex;flex-direction:column;justify-content:center;align-items:center;width:100%;min-height:44px;min-width:44px;padding:8px;border:3px solid #c4a873;border-radius:15px;background:#fffdf4;cursor:pointer;color:var(--ink);font:700 17px var(--f-body);transition:border-color .2s,background .2s}.md-picture{display:grid;place-items:center;width:100%;min-width:0}.md-picture img{max-width:100%;max-height:min(52dvh,480px);width:auto;object-fit:contain;object-position:center}.md-picture .mp-vis{display:block;padding:0}.md-picture .mp-visc{padding:0;border:0;background:none}.md-observe.observing{border-color:#c7891b;background:#ffe9a7;box-shadow:0 4px 0 #c79d51}.md-observe:focus-visible{outline:3px solid #248db8;outline-offset:2px}.md-svg{width:100%;max-height:180px;overflow:visible}.md-note{margin:6px 0 0;font-size:14px}.md-shape-board{position:relative;height:300px}.md-position{position:absolute;min-width:44px;min-height:44px}.md-position .md-observe{height:100%;padding:2px}.md-position .md-picture{height:100%}.md-position .md-svg{height:100%}.md-pictogram section{display:grid;grid-template-columns:70px 1fr;gap:8px;padding:8px;border-top:2px solid #d3bd92}.md-pictogram section>div{display:flex;flex-wrap:wrap;gap:4px}.md-pictogram output{grid-column:2;font-size:14px}.md-count{width:48px;height:48px;padding:2px}.md-count img{width:40px;height:40px}.md-teaching-steps{margin:14px 0;padding:0;list-style:none;display:grid;gap:8px;counter-reset:lesson-step}.md-teaching-steps li{position:relative;padding:10px 10px 10px 44px;border:2px solid #b9c99f;border-radius:12px;background:#f0f7df;font:600 16px/1.6 var(--f-body);animation:mdStepIn .3s var(--step-delay) both;counter-increment:lesson-step}.md-teaching-steps li:before{content:counter(lesson-step);position:absolute;left:8px;top:10px;width:26px;height:26px;display:grid;place-items:center;border:2px solid var(--ink);border-radius:50%;background:#ffe38a;font:800 17px var(--f-num)}@keyframes mdStepIn{from{opacity:0;translate:0 8px}to{opacity:1;translate:0 0}}.md-write-card{white-space:normal;line-height:2}.md-write-slot{display:inline-flex;flex-direction:column;vertical-align:middle;min-width:100px;max-width:100%;margin:5px;padding:4px 8px}.md-write-slot input{min-height:48px;max-width:100%;width:160px;padding:6px;border:2px solid #ab8455;border-radius:9px;background:#fff;font:500 20px var(--f-body);color:var(--ink);user-select:text}.md-blank-label{font-size:13px;line-height:1.5}.md-write-status{font-size:15px}.md-write-image{display:block;max-width:100%;max-height:min(52dvh,480px);width:auto;height:auto;object-fit:contain;object-position:center;margin:auto}
@media(max-width:600px){.md-cards{grid-template-columns:repeat(2,minmax(0,1fr));gap:6px}.md-observe{font-size:14px;padding:5px}.md-picture img,.md-write-image{max-height:min(40dvh,280px)}.md-board{padding:7px}.md-teaching-steps li{font-size:14px}.md-write-slot input{font-size:18px;width:130px}.md-shape-board{height:250px}.md-pictogram section{grid-template-columns:50px 1fr}}
@media(prefers-reduced-motion:reduce){.md-teaching-steps li{animation:none}.md-observe{transition:none}}

.md-step-next,.md-demo-next{display:none!important}.md-step-now{background:#ffe39b!important;border-color:#aa722b!important;box-shadow:0 3px 0 #c19b50}.md-fractions .observing svg{filter:drop-shadow(0 0 4px #eebc42)}

.md-count-groups{display:flex;flex-wrap:wrap;gap:14px}.md-count-groups section{flex:1;min-width:210px;padding:8px;border:2px solid #c7b186;border-radius:15px}.md-count-bundles{display:flex;flex-wrap:wrap;gap:6px}.md-object-group{display:flex;flex-wrap:wrap;gap:3px;max-width:230px;padding:5px;border:2px dashed #b8a37b;border-radius:12px}.md-ring{position:relative;width:204px;height:204px;flex:none}.md-ring .md-count{position:absolute;transform:translate(-50%,-50%)}.md-countnote{font-size:14px}.md-count[aria-pressed=true]{background:#8bd8c4}

.md-option-diagram{width:100%;min-width:100px;max-width:220px;display:grid;place-items:center}.md-option-diagram .md-cards{display:block;width:100%}.md-option-diagram .md-note{display:none}.md-option-diagram .md-svg{height:145px}.md-option-diagram .md-observe{display:block;border:0;background:none;padding:2px;pointer-events:none}.md-option-diagram .md-picture{display:block}

.md-text-card{font-size:clamp(24px,4vw,48px);padding:24px}.md-money-group{display:flex;flex-wrap:wrap;justify-content:center;gap:8px}.md-money-group img{width:74px!important;height:60px!important;object-fit:contain}.md-shade-stage{max-width:340px;width:100%;margin:16px auto}.md-shade-stage svg{width:100%;max-height:340px}.md-shade-stage [role=button]{cursor:pointer;transition:fill .2s,filter .2s}.md-shade-stage [role=button]:hover{filter:brightness(1.08)}.md-shade-stage [role=button]:focus{outline:3px solid #bc6e2b}.md-diagram-node{display:flex!important;flex-direction:column;height:auto!important;min-height:124px}.md-node-diagram{display:block;width:100%;max-width:250px}.md-node-diagram svg{width:100%;max-height:120px}.md-option-diagram .md-money-group{max-width:290px}.md-option-diagram .md-money-group img{width:52px!important;height:52px!important}

.md-piece-set{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}.md-piece{position:relative;display:block;min-width:80px;min-height:80px;border:3px solid var(--ink,#2b1d14);border-radius:18px;background:#fff9e8;overflow:hidden;cursor:pointer}.md-piece img{display:block;width:100%;height:130px;object-fit:contain}.md-piece i{position:absolute;inset:0;pointer-events:none;background:var(--piece-color);opacity:0;transition:opacity .25s,transform .25s;transform:scale(.5)}.md-piece-shaded i{opacity:.45;transform:scale(1)}.md-piece-shaded:after{content:"✓";position:absolute;right:6px;top:3px;color:#2b1d14;font-size:28px;font-weight:900}

.md-compare .md-picture{height:190px;display:flex;align-items:flex-end;justify-content:center}.md-compare .md-picture img{height:180px!important;object-fit:contain;transform-origin:bottom center}.md-calendar{display:flex;flex-direction:column;align-items:center;border:3px solid #2b1d14;border-radius:12px;overflow:hidden;background:#fff9e8}.md-calendar b{padding:8px;background:#ffc94f;width:100%;text-align:center}.md-calendar strong{font-size:64px;line-height:1.3}.md-calendar span{padding:8px}

.md-object-scene{display:flex;flex-wrap:wrap;justify-content:center;align-items:center;gap:8px;position:relative;padding:10px 56px 20px 10px}.md-object-sprite{width:82px!important;height:90px!important;object-fit:contain}.md-original-mark{position:absolute;right:4px;bottom:4px;width:46px!important;height:46px!important;object-fit:contain;font-size:44px;color:#2b1d14}.md-feature-map{display:grid;gap:12px;place-items:center;padding:12px}.md-feature-map>img{width:160px!important;height:170px!important;object-fit:contain}.md-feature-map>div{display:flex;flex-wrap:wrap;justify-content:center;gap:10px}.md-feature-map span{border:2px solid #78562e;background:#fff4cb;border-radius:30px;padding:8px 14px;font-weight:800}

.md-balance{position:relative;width:100%;max-width:440px;aspect-ratio:5/3;margin:auto}.md-balance>svg{position:absolute;inset:0;width:100%;height:100%}.md-pan{position:absolute;z-index:1;display:flex;justify-content:center;align-items:flex-end;flex-wrap:wrap;gap:2px;width:35%;height:44%;top:8%}.md-pan-left{left:2%;transform:translateY(calc(var(--tilt)*20px))}.md-pan-right{right:2%;transform:translateY(calc(var(--tilt)*-20px))}.md-pan img{width:30%!important;max-height:48%;object-fit:contain}.md-pan b{font-size:32px;background:#ffe6a0;border:3px solid #2b1d14;padding:5px 16px;border-radius:10px}.md-balance:hover .md-pan{filter:brightness(1.05)}

.md-piece-strip{grid-template-columns:repeat(4,minmax(0,1fr))}.md-piece-strip .md-piece{min-width:0}.md-piece-strip .md-piece img{height:90px}.md-quantity-relation{display:grid;grid-template-columns:1fr auto 2fr;gap:12px;align-items:center}.md-quantity-relation>div{display:flex;flex-wrap:wrap;justify-content:center;gap:6px}.md-quantity-relation img{width:54px!important;height:70px!important;object-fit:contain}.md-quantity-relation>div:first-child img{width:90px!important;height:120px!important}.md-quantity-relation>b{font-size:28px}

.md-givens{background:#fff1c5;border:3px solid #936632;border-radius:16px;padding:12px 16px;margin-bottom:14px;line-height:1.65}.md-givens>b{font-size:15px;color:#78562e}.md-givens p{margin:4px 0;font-weight:700}.md-demo-frames{padding:14px;border:3px solid #936632;border-radius:18px;background:#fff9e8;margin:12px 0}.md-demo-picture{animation:mdReveal .28s ease}.md-demo-frames p{font-weight:800;line-height:1.6}.md-piece.observing{outline:4px solid #c282dc;outline-offset:2px}.md-demo-picture .md-piece{min-width:0}.md-demo-picture .md-piece img{height:90px}
.md-source-svg{display:block;width:100%;max-height:390px;overflow:visible}.md-source-svg [data-part]{cursor:pointer;transition:filter .2s,fill .2s}.md-source-svg [data-part][aria-pressed=true]{filter:drop-shadow(0 0 4px #ffc243)}.md-route[aria-pressed=true]{stroke-width:19}.md-experiment{display:grid;grid-template-columns:1fr 1fr;gap:12px}.md-experiment section{background:#fff8e4;border:3px solid var(--ink);border-radius:18px;padding:10px}.md-experiment h4{text-align:center;margin:0 0 10px}.md-experiment svg{max-height:440px}.md-water-level{animation:md-water-appear .8s ease-out}@keyframes md-water-appear{from{opacity:.2}to{opacity:.85}}@media(max-width:600px){.md-experiment{grid-template-columns:1fr}.md-source-svg{max-height:330px}}
.md-experiment section{overflow:auto}.md-zoom .md-experiment svg{min-width:600px;max-height:none}.md-zoom-toggle{margin-bottom:12px}.md-magnet-lab{margin:18px 0;padding:14px;border:3px solid var(--ink);border-radius:20px;background:#fff8df}.md-magnet-lab h4{margin:0}.md-lab-track{position:relative;width:340px;max-width:100%;height:105px;border-bottom:4px solid #8d6944;touch-action:none}.md-lab-fixed,.md-lab-magnet{position:absolute;top:16px;width:115px;height:70px;padding:0;border:0;background:transparent}.md-lab-fixed{left:18px}.md-lab-magnet{cursor:grab;touch-action:none;transition:left .45s cubic-bezier(.2,.8,.2,1)}.md-lab-magnet.dragging{transition:none;cursor:grabbing}.md-lab-track img{width:100%;height:100%;object-fit:contain;pointer-events:none}.md-lab-track b{position:absolute;top:26px;left:15px;color:white;text-shadow:1px 1px #2b1d14;pointer-events:none}.md-lab-track b:last-child{left:auto;right:15px}.md-pole-reverse img{transform:scaleX(-1)}.md-lab-status{min-height:2.8em;font-weight:700}@media(prefers-reduced-motion:reduce){.md-lab-magnet,.md-water-level{transition:none;animation:none}}

.md-lab-fixed,.md-lab-magnet{width:33.8%}.md-lab-fixed{left:5.3%}
.bk-prow>div{min-width:0;flex:1}.bk-prow .md-source-svg,.bk-prow .md-svg{max-height:190px}.bk-prow .md-cards{min-width:0}
.md-node-diagram{position:relative}.md-node-zoom{min-width:44px;min-height:44px;border:2px solid var(--ink);border-radius:12px;background:#fff2b5;color:var(--ink);font:inherit;font-size:14px;font-weight:800;cursor:pointer}.md-figure-lightbox{position:fixed;inset:0;z-index:10000;display:grid;place-items:center;padding:18px;background:#2b1d14bb}.md-figure-lightbox>section{width:min(850px,100%);max-height:92dvh;overflow:auto;border:4px solid var(--ink);border-radius:22px;background:#fff8e4;padding:14px}.md-close-figure{position:sticky;top:0;z-index:2}.md-large-figure{overflow:auto}.md-large-figure>.md-svg,.md-large-figure>.md-source-svg{width:100%;min-width:540px;max-height:none}.md-figure-lightbox p{font-size:14px}.md-large-figure .md-money-group img{width:160px!important;height:120px!important}
.md-node-diagram.md-labeled-node .md-svg{height:auto;max-height:190px;width:100%}

/* Source-restored money operations and the root/leaf needs diagram. */
.md-money-item{position:relative;display:inline-flex;align-items:center;justify-content:center;max-width:100%}.md-money-item img{max-width:100%}.md-money-crossed i{position:absolute;inset:0;display:grid;place-items:center;font:800 80px/1 var(--f-num);color:#7a3330;text-shadow:0 1px #fff;pointer-events:none}.md-money-column{min-width:140px;max-width:100%;font:800 26px/1.6 var(--f-num);text-align:right}.md-money-column>div{display:flex;justify-content:flex-end;gap:16px}.md-money-total{border-top:3px solid var(--ink);margin-top:4px}.md-needs-svg{display:block;width:100%;max-height:360px}.md-needs-flow{opacity:.32}.md-needs-active{opacity:1}.md-needs-active .md-flow-line{stroke-dasharray:10 8;animation:mdNeedsFlow 1.4s linear infinite}@keyframes mdNeedsFlow{to{stroke-dashoffset:-36}}@media(max-width:600px){.md-money-column{font-size:21px;min-width:110px}.md-money-crossed i{font-size:55px}}@media(prefers-reduced-motion:reduce){.md-needs-active .md-flow-line{animation:none;stroke-dasharray:none}}

/* B19 (T19-D02): pictures that are compared by size stay in one row, in reading order, bottom-aligned ("从左到右"). */
.md-cards.md-compare[style*="--md-n"],body.study-window #qarea .md-cards.md-compare[style*="--md-n"]{grid-template-columns:repeat(var(--md-n),minmax(0,1fr))}.md-cards.md-compare[style*="--md-n"] .md-picture,body[data-view=game] #qarea .md-cards.md-compare[style*="--md-n"] .md-picture{height:128px;grid-template-rows:128px auto}.md-cards.md-compare[style*="--md-n"] .md-picture img,body[data-view=game] #qarea .md-cards.md-compare[style*="--md-n"] .md-picture img{max-width:100%;height:120px!important;object-position:50% 100%}
@media(max-width:600px){.md-cards.md-compare[style*="--md-n"],body.study-window #qarea .md-cards.md-compare[style*="--md-n"]{gap:4px}.md-cards.md-compare[style*="--md-n"] .md-picture,body[data-view=game] #qarea .md-cards.md-compare[style*="--md-n"] .md-picture{height:96px;grid-template-rows:96px auto}.md-cards.md-compare[style*="--md-n"] .md-picture img,body[data-view=game] #qarea .md-cards.md-compare[style*="--md-n"] .md-picture img{height:90px!important}}