@import url('https://fonts.googleapis.com/css2?family=Golos+Text:wght@400;500;600;700;800&display=swap');
:root{--paper:#faf9f6;--ink:#202622;--muted:#586054;--line:#dedfd7;--sage:#dbe5d5;--lilac:#e4dff2;--peach:#f4bea0;--yellow:#f5e9b9}*{box-sizing:border-box}body{margin:0;background:var(--paper);color:var(--ink);font:16px/1.5 'Golos Text',Arial,sans-serif}button,select,input{font:inherit;color:inherit}button,a,select,input{touch-action:manipulation}button,select{min-height:44px;border:1px solid var(--line);border-radius:24px;padding:10px 18px;background:transparent;cursor:pointer}button:hover:not(:disabled){background:#eaece5}button:disabled{opacity:.4;cursor:default}button.dark{background:var(--ink);color:var(--paper);border-color:var(--ink)}button.dark:hover:not(:disabled){background:#41483e}button[aria-pressed=true],button.selected{background:var(--lilac);border-color:#6c5887}a{color:inherit}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible,summary:focus-visible{outline:3px solid #675081;outline-offset:4px}header{height:78px;display:flex;align-items:center;gap:24px;padding:0 28px;border-bottom:1px solid var(--line)}.brand{display:flex;gap:10px;align-items:center;font-size:21px;font-weight:700;letter-spacing:-.7px;text-decoration:none}.mark{width:36px;height:36px;display:grid;place-items:center;border-radius:12px;background:var(--ink);color:var(--peach);font-size:26px}.collection{font-size:13px;text-decoration:none;color:var(--muted)}.toolbar{margin-left:auto;display:flex;align-items:center;gap:8px;font-size:13px}.locale select{appearance:none;padding:10px 36px 10px 15px;background:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='10' height='6' viewBox='0 0 10 6'%3E%3Cpath d='m1 1 4 4 4-4' fill='none' stroke='%23202622' stroke-width='1.5'/%3E%3C/svg%3E") no-repeat right 14px center}.layout{display:grid;grid-template-columns:238px minmax(0,1fr);min-height:calc(100dvh - 78px)}.rail{padding:30px 18px;border-right:1px solid var(--line);display:flex;flex-direction:column}.eyebrow{text-transform:uppercase;font-size:11px;font-weight:600;letter-spacing:1.5px;color:var(--muted)}.rail>.eyebrow{padding:0 14px}nav{display:grid;gap:5px}.chapter{display:flex;gap:13px;align-items:center;text-align:left;border:0;border-radius:14px;padding:12px 14px;width:100%;font-size:13px}.chapter span:first-child{color:var(--muted);font-size:11px;min-width:19px}.chapter[aria-current=step]{background:var(--lilac);font-weight:600}.rail-foot{margin-top:auto;padding:40px 14px 0;font-size:12px;color:var(--muted)}.rail-foot p{font-size:23px;letter-spacing:-1px;color:var(--ink);max-width:150px}.workspace{display:flex;flex-direction:column;min-width:0}main{padding:30px clamp(24px,4vw,72px) 32px;max-width:1400px;width:100%;margin:auto;flex:1;outline:none}.meta{display:flex;justify-content:space-between;gap:16px;font-size:12px;color:var(--muted);margin-bottom:22px}.meta span:first-child{text-transform:uppercase;letter-spacing:1px}h1{font-size:clamp(34px,3.7vw,58px);line-height:1.07;font-weight:600;letter-spacing:-2px;margin:0 0 18px;max-width:950px}.lead{font-size:clamp(17px,1.6vw,22px);color:var(--muted);margin:0 0 26px;max-width:850px}.panel{border-radius:24px;background:var(--sage);padding:clamp(22px,3vw,42px)}.panel.lilac{background:var(--lilac)}.panel.peach{background:#faeadf}.split{display:grid;grid-template-columns:1fr 1fr;gap:22px}.equation{font-variant-numeric:tabular-nums;font-size:clamp(28px,4vw,62px);line-height:1.45;letter-spacing:-1.5px;font-weight:600;overflow-wrap:anywhere}.equation.small{font-size:clamp(25px,3vw,42px)}.actions{display:flex;flex-wrap:wrap;gap:10px;align-items:center;margin-top:22px}.prompt{font-size:18px;margin:0 0 18px}.feedback{margin-top:18px;padding:15px 18px;border-radius:14px;border:1px solid #65705b;background:#fff9;line-height:1.6;font-size:17px}.feedback.error{border-color:#a35135;background:#fff1e8}.feedback:empty{display:none}.task label{display:block;font-size:15px;font-weight:500}.task input{width:100%;max-width:240px;min-height:55px;background:#fff9;border:1px solid #839078;border-radius:13px;padding:12px 16px;font-size:22px;margin-top:12px}.task input:focus{background:#fff}.task-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:16px}.task-grid.two{grid-template-columns:repeat(2,minmax(0,1fr))}.task-grid .panel{padding:24px}.source{font-size:12px;color:var(--muted);margin:20px 0 0}.badge{font-size:12px;display:inline-block;border:1px solid #ffffff80;border-radius:20px;padding:5px 12px;margin-bottom:15px}.tiles{display:flex;flex-wrap:wrap;align-items:center;gap:12px;font-size:32px}.numtile{padding:18px 23px;min-width:88px;border-radius:18px;background:var(--paper);border:1px solid #b8c2b2;font-size:clamp(27px,4vw,52px);font-weight:700}.numtile[aria-pressed=true]{background:var(--ink);color:var(--paper)}.term{min-width:115px;display:flex;flex-direction:column;align-items:center;gap:14px;background:#ffffff70;padding:20px;border-radius:20px}.term strong{font-size:52px;line-height:1.2}.term small{font-size:13px}.block-groups{display:flex;gap:12px;align-items:center;justify-content:center;flex-wrap:wrap;margin:20px 0}.group{padding:17px 22px;border-radius:18px;border:2px solid #86977c;background:#ffffff80;font-size:36px;font-weight:600}.group.lilac{border-color:#9880b4}.dots{display:grid;grid-template-columns:repeat(8,9px);gap:5px;margin-top:15px;min-height:52px}.dot{background:var(--ink);width:9px;height:9px;border-radius:50%}.group-frame{display:flex;gap:12px;align-items:center;padding:16px;border:2px solid #6d5c85;border-radius:22px}.operators{font-size:30px}.law{font-size:clamp(24px,3.6vw,44px);font-weight:600;margin:20px 0 0}.note{color:var(--muted);font-size:15px}.zero{display:flex;align-items:center;gap:20px;flex-wrap:wrap}.zero .empty{height:80px;width:110px;border:2px dashed #788572;border-radius:18px;display:grid;place-items:center;font-size:28px}.practice-top{display:flex;justify-content:space-between;gap:20px}.hint{margin-top:12px;border-top:1px solid #a6af9e;padding-top:12px}.hint summary,details summary{cursor:pointer;font-size:15px}.hint p{font-size:16px}.challenge{margin-top:22px;padding:20px 24px;border:1px solid var(--line);border-radius:18px}.challenge summary{font-weight:600}.challenge .equation{margin-top:20px}.exit-reason{margin-top:18px}.exit-reason button{margin:6px 6px 6px 0}.intro-note{font-size:14px;color:var(--muted)}footer{border-top:1px solid var(--line);padding:20px 28px;display:flex;align-items:center;gap:20px;margin-top:auto;font-size:13px}.position{display:flex;align-items:center;gap:15px;margin-right:auto;min-width:100px}.track{width:90px;height:3px;background:var(--line)}#progress-fill{height:100%;background:var(--ink);transition:width .25s}.footer-buttons{display:flex;gap:10px}#reset-button{font-size:12px;border:0;padding:10px}.teacher-drawer{position:fixed;right:0;top:0;bottom:0;width:min(610px,100vw);background:white;box-shadow:-10px 0 70px #0002;padding:26px;overflow-y:auto;z-index:100}.teacher-drawer[hidden]{display:none}.drawer-head{display:flex;justify-content:space-between;gap:20px;align-items:flex-start;margin-bottom:22px}.drawer-head h2{font-size:24px;margin:5px 0}.close{font-size:25px;padding:0;width:44px;flex-shrink:0}dialog{width:min(540px,94vw);border:1px solid var(--line);border-radius:22px;padding:24px}dialog::backdrop{background:#20262255}#contents-button{display:none}.sr,.skip{position:absolute;width:1px;height:1px;padding:0;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.skip:focus{clip:auto;width:auto;height:auto;top:12px;left:12px;padding:12px;background:white;z-index:200}.presenting .rail,.presenting .collection{display:none}.presenting .layout{grid-template-columns:1fr}.presenting main{max-width:1360px}.presenting header{height:66px}.presenting .layout{min-height:calc(100dvh - 66px)}.presenting #contents-button{display:inline-block}.presenting h1{font-size:clamp(38px,4.3vw,68px)}.presenting .lead{font-size:23px}.presenting .task input{font-size:27px}.presenting .meta{font-size:14px}@media(min-width:1450px){main{padding-top:45px}}@media(max-width:1050px){.layout{grid-template-columns:200px minmax(0,1fr)}header{gap:14px;padding:0 18px}.toolbar{gap:5px;font-size:12px}.toolbar button{padding:10px 12px}.brand{font-size:18px}.collection{display:none}.task-grid{grid-template-columns:1fr}.task-grid .panel{padding:20px}.task-grid .task{display:grid;grid-template-columns:1fr 1fr;gap:12px;align-items:center}.task input{margin:0}.task .feedback{grid-column:1/-1;margin:0}.task .badge{display:none}.task .equation{font-size:28px}.task .hint{grid-column:1/-1}.term{min-width:80px;padding:16px}.term strong{font-size:40px}}@media(max-width:740px){header{height:auto;min-height:116px;flex-wrap:wrap;gap:12px;padding:14px 18px}.brand{margin-right:auto}.toolbar{width:100%;margin:0;gap:6px;justify-content:space-between}.toolbar button{padding:9px 12px;font-size:12px}.locale select{padding-left:12px;padding-right:30px;background-position:right 11px center}.layout{display:block;min-height:calc(100dvh - 116px)}.rail{display:none}#contents-button{display:inline-block}.workspace{min-height:calc(100dvh - 116px)}main{padding:24px 20px}.meta{font-size:10px;gap:10px;margin-bottom:18px}.meta span:first-child{max-width:70%}h1{font-size:36px;letter-spacing:-1.4px}.lead{font-size:18px}.split,.task-grid.two{grid-template-columns:1fr}.task-grid .task{display:block}.task input{margin-top:12px;max-width:none}.task .feedback{margin-top:12px}.task-grid{gap:12px}.tiles{gap:8px}.numtile{min-width:66px;padding:14px 17px;font-size:32px}.term{min-width:70px;padding:15px 12px}.term strong{font-size:35px}.term small{font-size:12px}.equation{font-size:34px}.equation.small{font-size:29px}.operators{font-size:24px}.group{font-size:28px;padding:12px}.group-frame{padding:10px;gap:8px}.dots{grid-template-columns:repeat(8,6px);gap:3px}.dot{width:6px;height:6px}.block-groups{gap:8px}.law{font-size:27px}.panel{padding:22px}.actions button{font-size:14px}footer{padding:16px 20px;gap:12px;flex-wrap:wrap}.position{min-width:80px;gap:10px}.track{width:55px}.footer-buttons{margin-left:auto}#reset-button{order:3;width:100%;padding:5px;min-height:35px}.presenting header{height:auto}.presenting .layout,.presenting .workspace{min-height:calc(100dvh - 116px)}.presenting h1{font-size:38px}.presenting .lead{font-size:19px}.teacher-drawer{padding:22px}.practice-top{display:block}}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation:none!important;transition:none!important;scroll-behavior:auto!important}}
@media(max-width:740px){.toolbar{flex-wrap:wrap;justify-content:flex-start}.toolbar .locale{margin-right:auto}.toolbar button{max-width:100%;white-space:normal}header{min-height:116px;height:auto}.meta>span{min-width:0}#main .equation{overflow-wrap:anywhere}}
.written-model{background:var(--sage);border-radius:24px;padding:24px;outline-offset:5px}.written-progress{display:flex;align-items:center;justify-content:space-between;font-size:13px;color:var(--muted)}.written-progress .badge{margin:0}.written-scroll{overflow-x:auto;overscroll-behavior-x:contain;margin-top:10px}.written-svg{display:block;width:100%;min-width:760px;min-height:250px;font-family:'Golos Text',Arial,sans-serif;font-variant-numeric:tabular-nums;font-size:33px;font-weight:500;overflow:hidden}.written-svg g[data-part]{transform-origin:0 0;transform-box:view-box;opacity:0}.written-svg .original,.written-svg .result{font-size:44px;font-weight:600}.written-svg .tens{fill:#70442b}.written-svg .carry-one{font-size:26px;fill:#70442b}.written-svg .exchange{fill:#70442b;font-size:26px}.written-svg .carry-caption{font-size:21px}.written-description{font-size:clamp(18px,1.9vw,25px);line-height:1.4;min-height:2.8em;max-width:1000px;margin:18px 0}.written-controls{display:flex;flex-wrap:wrap;gap:10px}.written-controls button{font-size:14px;background:#ffffff60}.written-controls button.dark{background:var(--ink)}.written-controls [hidden],.written-question[hidden]{display:none!important}.written-scroll-hint{display:none}.written-question{margin-top:24px;border-top:1px solid #adb9a6;padding-top:20px}.written-question summary{font-size:18px}.written-question p{font-size:18px}@media(max-width:1000px){.written-scroll-hint{display:block;font-size:12px}.written-model{padding:18px}.written-description{min-height:4em}.written-controls button{white-space:normal;max-width:100%}}@media(prefers-reduced-motion:reduce){.written-svg{scroll-behavior:auto}}