.subtraction-board{padding:20px;background:radial-gradient(ellipse at 50% 35%,#f4f2ff,white 75%)}.place-equation{text-align:center;font-size:26px;padding:6px 0 22px}.place-lanes{display:grid;grid-template-columns:repeat(var(--columns),minmax(0,1fr));gap:10px}.place-lane{border:1px solid #e5e3f1;background:#fafaff;border-radius:13px;min-width:0;display:flex;flex-direction:column;padding:12px 9px;transition:background .2s,box-shadow .2s}.place-lane.over{background:#ede9ff;box-shadow:0 0 0 3px #c8c0fa}.place-title{text-align:center;text-transform:uppercase;font:10px 'DM Mono',monospace;letter-spacing:.06em;color:#807991}.place-count{text-align:center;font:500 28px 'Fraunces',serif;padding:5px;color:#51497b}.place-chips{display:flex;flex-wrap:wrap;justify-content:center;align-content:flex-start;gap:5px;min-height:100px;padding:8px 0;flex:1}.place-chip{height:13px;width:17px;background:#bab3ee;border:1px solid #aba1e1;border-radius:3px;box-shadow:0 2px 3px #594a9810}.place-chip.whole{height:23px;width:25px;background:linear-gradient(130deg,#b6acee,#8b7dc8)}.place-chip.tenth{width:23px;background:#a094dc}.place-chip.hundredth{height:10px;width:12px;background:#bfb6d8}.place-chip.new{animation:enter .4s ease}.place-action{border:1px solid #d9d3f3;background:white;color:#625185;border-radius:9px;padding:9px 6px;margin-top:7px;font-size:11px;line-height:1.4;touch-action:none;cursor:grab;position:relative}.place-action.remove{background:#fff6e8;border-color:#efdbb9;color:#8a612f}.place-action[aria-pressed=true]{outline:2px solid #a699d0;outline-offset:2px}.place-action.dragging{z-index:8;box-shadow:0 12px 22px #463b8928;cursor:grabbing}.place-drop{border:1px dashed #c6bfd9;background:#fff;min-height:52px;border-radius:10px;color:#7f7598;width:100%;font-size:11px;line-height:1.5;padding:7px;margin-top:8px}.place-drop.over{background:#e7e1fa;border-color:#8974b2}.removed-tray{width:100%;border:1px dashed #d4b780;background:#fffaf0;color:#85632e;border-radius:12px;padding:16px;margin-top:16px;text-align:center;font-size:12px;min-height:65px}.removed-tray.over{background:#faedcf;box-shadow:0 0 0 3px #edcf9850}.regroup-record{font-size:13px;text-align:center;color:#65597f;padding:18px 0 0;min-height:60px}.sub-model-controls{padding:14px 22px;display:flex;gap:8px;border-top:1px solid var(--line)}.sub-ledger{padding:0 22px 16px}.sub-ledger p{font-size:12px;color:var(--muted);margin:8px 0}.sub-ledger .math{font-size:18px}.skill-links{display:flex;flex-wrap:wrap;gap:10px;margin:20px 0}.skill-links a{font-size:13px;text-decoration:none;padding:9px 13px;border:1px solid var(--line);border-radius:10px;background:white}.subtopic-skill{display:block;background:#fff;border:1px solid var(--line);border-radius:13px;padding:18px 20px;margin:12px 0;color:var(--ink);text-decoration:none}.subtopic-skill strong{font-size:17px}.subtopic-skill p{font-size:13px;color:var(--muted);margin:6px 0}.subtopic-skill.ready{border-left:3px solid #8a7ce2}.subtopic-skill .eyebrow{margin-bottom:8px}.written-columns{font-family:'DM Mono',monospace;background:#f6f5fb;padding:16px;border-radius:10px;text-align:right;font-size:20px;max-width:240px;margin:12px auto;white-space:pre}.sub-select{font-size:13px;border:1px solid var(--line);padding:7px 9px;border-radius:8px;background:white;max-width:100%}@media(max-width:440px){.subtraction-board{padding:15px 10px}.place-lanes{gap:7px}.place-lane{padding:10px 6px}.place-action{font-size:10px}.place-chip.whole{width:21px;height:22px}.place-title{font-size:9px;letter-spacing:0}.place-chips{gap:4px;min-height:85px}.place-equation{font-size:23px}}
.place-chip.new{animation:piece-exchange .42s cubic-bezier(.2,.7,.2,1) both}.removed-tray.received{animation:tray-receive .55s ease}@keyframes piece-exchange{from{opacity:0;transform:translate(-15px,-9px) scale(.35)}to{opacity:1;transform:translate(0,0) scale(1)}}@keyframes tray-receive{0%,100%{background:#fffaf0}40%{background:#f5e5c3}}
/* Written algorithm replaces the multi-destination drag workbench. */
.column-prompt{text-align:center;font-size:13px;color:#62577d;margin:5px 0 25px}.written-subtraction{display:grid;grid-template-columns:22px repeat(var(--places),minmax(0,1fr));gap:0;max-width:390px;margin:0 auto 25px}.written-place{font:10px 'DM Mono',monospace;text-align:center;color:#837a95;padding-bottom:15px}.written-sign{align-self:center;text-align:center;color:#8c83a0;font-size:27px}.written-digit{position:relative;text-align:center;padding:17px 5px;font:500 37px 'Fraunces',serif;border:1px solid transparent;background:transparent;color:#33304e;min-height:84px}.written-digit.active{background:#f0edfc}.written-digit.exchange{background:#fff1db;border:1px solid #e9cd9b;border-radius:12px;color:#875a23;cursor:pointer}.previous-digit{font:14px 'DM Sans',sans-serif;position:absolute;top:0;left:25%;color:#a49ab2}.written-point{position:absolute;right:-5px;bottom:17px;z-index:2}.written-result .written-point{bottom:5px}.subtrahend{border-bottom:2px solid #aaa0bd}.written-rule{border-top:2px solid #aaa0bd}.written-result{position:relative;text-align:center;font:500 36px 'Fraunces',serif;padding:9px 5px;color:#5f5598;border-top:2px solid #aaa0bd;min-height:68px}.column-explanation{font-size:14px;text-align:center;color:#655c78;max-width:370px;margin:16px auto}.column-next{display:block;margin:18px auto 0}.exchanged{animation:exchange-digit .4s ease}@keyframes exchange-digit{from{background:#f6dfb6;transform:translateY(-4px)}to{transform:translateY(0)}}