:root{--ink:#1f2547;--muted:#5d6385;--bg:#f6f4ff;--card:#fff;--brand:#2f3a8f;--brand-2:#4b5bd6;--accent:#ff7a59;--earth:#22a699;--gold:#ffc93c;--ok:#1d8a5b;--ok-bg:#e3f7ec;--warn:#b4441f;--warn-bg:#fff0e8;--info-bg:#eef1ff;--radius:16px;--shadow:0 6px 24px #1f254714;color:var(--ink);background:var(--bg);-webkit-text-size-adjust:100%;font-family:Nunito,Segoe UI,system-ui,-apple-system,Roboto,Helvetica Neue,Arial,sans-serif;line-height:1.5}*{box-sizing:border-box}body{background:radial-gradient(1200px 500px at 10% -10%, #e7e3ff 0, transparent 60%), radial-gradient(900px 400px at 110% 0, #ffe9df 0, transparent 60%), var(--bg);min-height:100vh;margin:0}a{color:var(--brand-2)}.skip{position:absolute;left:-999px}.skip:focus{z-index:10;background:#fff;border-radius:8px;padding:8px 12px;top:8px;left:8px}:focus-visible{outline:3px solid var(--brand-2);outline-offset:2px}.top{flex-wrap:wrap;justify-content:space-between;align-items:center;gap:12px;max-width:1180px;margin:0 auto;padding:12px clamp(12px,4vw,32px);display:flex}.logo{color:var(--brand);align-items:center;gap:10px;font-size:1.25rem;font-weight:800;text-decoration:none;display:flex}.logo-mark{width:32px;height:32px}nav{box-shadow:var(--shadow);background:#fff;border-radius:999px;gap:4px;padding:4px;display:flex}nav a{color:var(--muted);border-radius:999px;padding:6px 14px;font-weight:700;text-decoration:none}nav a.active{background:var(--brand);color:#fff}main{max-width:1180px;margin:0 auto;padding:4px clamp(12px,4vw,32px) 48px}h1,h2{margin:.2em 0 .4em;line-height:1.2}.muted{color:var(--muted)}.center{text-align:center}.hero{text-align:center;padding:24px 0 8px}.hero h1{color:var(--brand);font-size:clamp(1.7rem,5vw,2.6rem)}.hero p{max-width:640px;color:var(--muted);margin:0 auto 20px;font-size:1.1rem}.lesson-list{grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:12px;margin:24px auto;padding:0;list-style:none;display:grid}.lesson-card{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);color:inherit;border:2px solid #0000;align-items:center;gap:14px;height:100%;padding:16px;text-decoration:none;transition:transform .15s,border-color .15s;display:flex}.lesson-card:hover{border-color:#d9dcff;transform:translateY(-2px)}.lesson-num{background:var(--info-bg);width:42px;height:42px;color:var(--brand);border-radius:50%;flex:none;place-items:center;font-weight:800;display:grid}.lesson-card.done .lesson-num{background:var(--ok-bg);color:var(--ok)}.lesson-text{flex-direction:column;display:flex}.lesson-text span{color:var(--muted);font-size:.95rem}.btn{min-height:44px;color:var(--ink);font:inherit;cursor:pointer;touch-action:manipulation;background:#fff;border:2px solid #dfe2f5;border-radius:12px;justify-content:center;align-items:center;gap:6px;padding:8px 16px;font-weight:700;text-decoration:none;display:inline-flex}.btn:hover{border-color:#c3c8ee}.btn:disabled{opacity:.45;cursor:not-allowed}.btn.primary{background:var(--brand);border-color:var(--brand);color:#fff}.btn.primary:hover{background:var(--brand-2);border-color:var(--brand-2)}.btn.big{padding:12px 26px;font-size:1.15rem}.btn.pulse{animation:1s ease-in-out infinite pulse}[hidden]{display:none!important}.layout{grid-template-columns:minmax(280px,400px) 1fr;align-items:start;gap:20px;display:grid}@media (width<=820px){.layout{grid-template-columns:1fr}.layout.practice .board{order:-1}}.panel,.board{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);padding:clamp(14px,3vw,24px)}.panel.narrow{max-width:720px;margin:0 auto 16px}.board{flex-direction:column;align-items:center;gap:12px;display:flex;position:relative;overflow:hidden}.board.wide{max-width:720px;margin:0 auto}.crumb{font-size:.95rem;font-weight:700;text-decoration:none}.lesson-title{color:var(--muted);font-size:1.2rem}.progress{background:#eceefe;border-radius:99px;height:8px;margin:8px 0 12px;overflow:hidden}.progress-fill{background:linear-gradient(90deg, var(--brand-2), var(--accent));width:0;height:100%;transition:width .3s}.step-meta{color:var(--muted);flex-wrap:wrap;align-items:center;gap:8px;font-size:.85rem;display:flex}.problem-tag{color:var(--ink);font-weight:700}.chip{background:var(--info-bg);color:var(--brand);white-space:nowrap;border-radius:99px;padding:2px 10px;font-size:.78rem;font-weight:800;display:inline-block}.chip.five-complement{color:#8a5a00;background:#fff4d6}.chip.ten-complement{color:#a33b18;background:#ffe6de}.chip.carry,.chip.borrow{color:#0f6f66;background:#e7f6f4}.chip.set{color:#5b3fb5;background:#f0ecff}.panel h2{font-size:1.45rem}.step-text{font-size:1.1rem}.why{border-left:4px solid var(--gold);color:var(--muted);background:#fafaff;border-radius:8px;padding:8px 12px}.feedback{border-radius:12px;min-height:0;margin:8px 0;font-weight:700}.feedback:empty{display:none}.feedback.ok,.feedback.info,.feedback.warn{padding:10px 14px}.feedback.ok{background:var(--ok-bg);color:var(--ok)}.feedback.info{background:var(--info-bg);color:var(--brand)}.feedback.warn{background:var(--warn-bg);color:var(--warn)}.actions{flex-wrap:wrap;gap:8px;margin-top:12px;display:flex}.actions .primary{margin-left:auto}.readout{align-items:baseline;gap:12px;display:flex}.readout-label{color:var(--muted);font-weight:700}.readout-num{color:var(--brand);font-variant-numeric:tabular-nums;min-width:2ch;font-size:clamp(2rem,7vw,2.8rem);font-weight:800}.abacus{--rw:min(68px, calc((100vw - 76px) / var(--rods)));--bh:clamp(26px, calc(var(--rw) * .52), 34px);--pad:8px;-webkit-user-select:none;user-select:none;-webkit-tap-highlight-color:transparent;width:max-content;max-width:100%}.frame{background:linear-gradient(180deg, #3c4aa8, var(--brand));border-radius:18px;padding:10px 12px 4px;box-shadow:inset 0 2px #ffffff26,0 10px 24px #2f3a8f40}.rods{grid-template-columns:repeat(var(--rods), var(--rw));background:#fbfaf5;border-radius:10px;display:grid;overflow:hidden}.rod{flex-direction:column;align-items:center;transition:background .2s;display:flex;position:relative}.rod.rod-hl{background:#fff6d8}.deck{width:100%;position:relative}.deck:before{content:"";background:#b8b3a6;border-radius:2px;width:4px;position:absolute;top:0;bottom:0;left:50%;transform:translate(-50%)}.deck.upper{height:calc(var(--bh) * 2 + var(--pad))}.deck.lower{height:calc(var(--bh) * 5 + var(--pad))}.beam{z-index:1;background:linear-gradient(#ffd978,#f2b632);width:100%;height:12px;position:relative;box-shadow:0 1px #c98f12}.unit-dot{background:#6b4a00;border-radius:50%;width:6px;height:6px;margin:-3px 0 0 -3px;position:absolute;top:50%;left:50%}.bead{width:calc(var(--rw) * .92);height:var(--bh);margin-left:calc(var(--rw) * -.46);cursor:pointer;touch-action:manipulation;transform:translateY(calc(var(--slot,0) * var(--bh)));z-index:2;background:0 0;border:0;border-radius:999px;padding:0;transition:transform .22s cubic-bezier(.3,.7,.4,1.2);position:absolute;top:0;left:50%}.deck.lower .bead{top:var(--pad)}.bead:before{content:"";clip-path:polygon(0 50%,20% 0,80% 0,100% 50%,80% 100%,20% 100%);background:var(--c);transition:background .2s;position:absolute;inset:2px 0}.bead.heaven{--c:linear-gradient(180deg, #ffd0c2, #f0b4a2)}.bead.heaven.active{--c:linear-gradient(180deg, #ff9a7d, #ff6b45 55%, #e2532f)}.bead.earth{--c:linear-gradient(180deg, #c5ebe6, #a9ddd6)}.bead.earth.active{--c:linear-gradient(180deg, #4fd1c1, #22a699 55%, #13877c)}.bead:hover:before{filter:brightness(1.06)}.bead.target:after{content:"";border:3px solid var(--gold);pointer-events:none;border-radius:999px;animation:1s ease-in-out infinite glow;position:absolute;inset:-2px -3px;box-shadow:0 0 12px #ffb900bf}.bead:focus-visible{outline:3px solid var(--brand-2);outline-offset:1px}.abacus.locked .bead{cursor:progress}.rod-digit{color:var(--brand);font-variant-numeric:tabular-nums;padding-top:4px;font-size:1.15rem;font-weight:800}.place{color:var(--muted);white-space:nowrap;padding-bottom:6px;font-size:.72rem;font-weight:700}.abacus[data-part=upper] .bead.heaven:after,.abacus[data-part=lower] .bead.earth:after{content:"";border:3px solid var(--gold);border-radius:999px;animation:1s ease-in-out infinite glow;position:absolute;inset:-2px -3px}.abacus[data-part=beam] .beam{outline:3px solid var(--gold);animation:1s ease-in-out infinite glow}.abacus[data-part=rods] .place,.abacus[data-part=rods] .rod-digit{background:#fff1c4;border-radius:6px;padding-left:4px;padding-right:4px}.help{color:var(--muted);align-self:stretch;font-size:.9rem}.help summary{cursor:pointer;font-weight:700}.field{margin:10px 0}.field-label{color:var(--muted);margin-bottom:4px;font-size:.85rem;font-weight:700;display:block}.segmented{background:#eef0fb;border-radius:12px;flex-wrap:wrap;gap:2px;padding:3px;display:inline-flex}.segmented button{font:inherit;min-height:40px;color:var(--muted);cursor:pointer;background:0 0;border:0;border-radius:10px;padding:8px 12px;font-weight:700}.segmented button.on{color:var(--brand);background:#fff;box-shadow:0 1px 4px #0000001a}.check{align-items:center;gap:8px;margin:8px 0;font-weight:600;display:flex}.check input{width:20px;height:20px}.question{color:var(--ink);font-variant-numeric:tabular-nums;margin:0;font-size:clamp(2rem,7vw,2.6rem);font-weight:800}.question .eq{color:var(--accent)}.step-list{align-self:stretch;margin:4px 0 0;padding-left:20px}.step-list li{opacity:.6;margin:6px 0}.step-list li.active{opacity:1;font-size:1.02rem}.step-list li.past{opacity:.85}.step-list:empty{display:none}.stats{margin-top:12px}.inline-form{flex-wrap:wrap;gap:8px;display:flex}.inline-form input{font:inherit;border:2px solid #dfe2f5;border-radius:12px;width:12ch;min-height:44px;padding:8px 12px}.confetti{pointer-events:none;position:absolute;top:45%;left:50%}.confetti i{border-radius:2px;width:8px;height:12px;animation:1.2s ease-out forwards pop;position:absolute}@keyframes pop{0%{opacity:1;transform:translate(0)rotate(0)}to{transform:translate(var(--x), calc(var(--y) + 260px)) rotate(var(--r));opacity:0}}@keyframes glow{50%{opacity:.45}}@keyframes pulse{50%{transform:scale(1.05)}}@media (prefers-reduced-motion:reduce){*,:before,:after{transition-duration:.01ms!important;animation-duration:.01ms!important;animation-iteration-count:1!important}}