@font-face{font-family:Lab;src:local("Trebuchet MS");font-display:swap}
:root{color-scheme:light;--navy:#09394a;--ink:#183d49;--muted:#536d75;--paper:#faf8f1;--line:#dce5df;--accent:#e45f40;--soft:#fff0e5;--teal:#197b75;--success:#126c50;--shadow:0 5px 0 #0b384a0c}
*{box-sizing:border-box}body{margin:0;background:var(--paper);color:var(--ink);font:16px Lab,"Trebuchet MS",Arial,sans-serif;line-height:1.55}.teal{--accent:#197b75;--soft:#e4f2ec}.purple{--accent:#7553a1;--soft:#f0e9f6}button,input,select{font:inherit}button,a,input,select{touch-action:manipulation}button{cursor:pointer}button:disabled{cursor:default;opacity:.5}a{color:inherit}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible{outline:3px solid #e9a837;outline-offset:4px}button,input,select{border-radius:10px}input,select{border:1px solid #afc4bc;background:#fff;padding:11px 13px;color:var(--navy);max-width:100%}input[type=number]{width:150px}input[type=range]{accent-color:var(--accent);padding:0;width:100%}label{display:block;font-weight:700;font-size:14px}label input,label select{margin-top:7px}p{margin:0 0 16px}h1,h2,h3{line-height:1.18;color:var(--navy)}h1{font-size:clamp(29px,3.7vw,46px);letter-spacing:-1.6px;margin:0 0 13px}h2{font-size:24px;letter-spacing:-.7px;margin:0 0 14px}h3{font-size:18px;margin:0 0 12px}small,.small{font-size:13px}.muted{color:var(--muted)}.lab-header,.lab-main,.lab-footer{width:min(1220px,calc(100% - 48px));margin-inline:auto}.lab-header{display:flex;align-items:center;gap:20px;min-height:91px;border-bottom:1px solid var(--line)}.brand img{display:block;width:155px;height:auto}.back-link{margin-left:auto;text-decoration:none;font-size:13px;font-weight:700}.icon-button{background:#fff;border:1px solid var(--line);font-size:24px;line-height:1;padding:10px 13px;color:var(--navy)}.lab-main{padding:32px 0 48px}.title-row{display:flex;align-items:center;justify-content:space-between;gap:25px;margin-bottom:25px}.eyebrow{font-size:10px;letter-spacing:1.8px;font-weight:800;color:var(--accent);margin:0 0 9px}.subtitle{font-size:16px;color:var(--muted);max-width:650px;margin:0}.studio-badge{font-size:11px;font-weight:700;border:1px solid var(--line);padding:11px 16px;border-radius:30px;background:#fff;white-space:nowrap}.tabs{display:flex;gap:5px;background:#e9eee8;padding:5px;border-radius:14px;width:max-content;max-width:100%;margin-bottom:24px;overflow-x:auto}.tab{border:0;background:transparent;padding:11px 20px;border-radius:10px;color:var(--muted);font-size:14px;font-weight:700;white-space:nowrap}.tab.active{color:var(--navy);background:#fff;box-shadow:0 2px 6px #103c4510}.workspace{display:grid;grid-template-columns:minmax(0,1fr) 285px;gap:22px;align-items:start}.panel{background:#fff;border:1px solid var(--line);border-radius:19px;padding:27px;box-shadow:var(--shadow);min-width:0}.panel.soft{background:var(--soft);box-shadow:none}.panel-heading{display:flex;align-items:flex-start;justify-content:space-between;gap:20px}.pill{display:inline-flex;padding:5px 10px;border-radius:30px;background:var(--soft);color:var(--accent);font-size:10px;font-weight:800;letter-spacing:.5px}.button{background:var(--navy);color:#fff;border:1px solid var(--navy);padding:11px 19px;font-weight:700;font-size:14px;box-shadow:0 3px 0 #062a39;min-height:45px}.button:hover{background:#155267}.button.secondary{background:#fff;color:var(--navy);border:1px solid #b5c9c0;box-shadow:0 3px 0 #e0e9e2}.button.accent{background:var(--accent);border-color:var(--accent);box-shadow:0 3px 0 color-mix(in srgb,var(--accent),black 22%)}.button.text{background:transparent;border:0;box-shadow:none;color:var(--muted);padding:7px 4px;min-height:30px;font-size:12px}.actions{display:flex;align-items:center;flex-wrap:wrap;gap:12px;margin-top:18px}.feedback{margin-top:18px;padding:13px 16px;border-radius:11px;background:#f0f4f1;color:var(--navy);font-size:14px;line-height:1.6;min-height:48px}.feedback.success{background:#e4f3e8;color:#12573e}.feedback.error{background:#fff0e1;color:#814012}.feedback:empty{display:none}.rule{display:flex;gap:12px;border-bottom:1px solid var(--line);padding:15px 0}.rule:last-child{border:0}.rule-number{display:grid;place-items:center;flex-shrink:0;width:29px;height:29px;border-radius:9px;background:#fff;border:1px solid var(--line);font-weight:700;color:var(--accent)}.rule p{margin:0;font-size:13px}.rule strong{display:block;font-size:15px;margin-bottom:4px}.rule.active .rule-number{background:var(--accent);color:white;border-color:var(--accent)}.side-note{font-size:12px;color:var(--muted);line-height:1.7;margin:18px 0 0}.separator{height:1px;background:var(--line);margin:23px 0}.expression{display:flex;flex-wrap:wrap;justify-content:center;align-items:center;gap:7px;min-height:118px;margin:24px 0;padding:22px 10px;border:1px solid var(--line);border-radius:15px;background:#fcfcf8}.token{font-size:clamp(20px,3vw,32px);font-weight:700;font-variant-numeric:tabular-nums;line-height:1.5;padding:3px 2px}.operation{border:1.5px solid #aac0b5;color:var(--navy);background:#fff;width:44px;min-height:46px;font-size:27px;font-weight:600;padding:0}.operation:hover{background:var(--soft);border-color:var(--accent)}.token.selected,.operation.selected{background:#ffe788;border-color:#cf9b22;border-radius:8px}.operation.hinted{outline:3px solid #e6ae35;outline-offset:3px}.answer-row{display:flex;align-items:flex-end;gap:12px;flex-wrap:wrap}.answer-row label{flex:1;min-width:150px}.answer-row input{width:100%}.working{list-style:none;padding:0;margin:15px 0 0;font-size:19px;font-variant-numeric:tabular-nums}.working li{border-top:1px dashed var(--line);padding:12px 0;display:flex;gap:11px;align-items:baseline;flex-wrap:wrap}.working .equal-sign{color:#8caaa0}.working small{margin-left:auto;color:var(--muted);font-size:11px}.working li:first-child{border-top:0}.progress-line{height:6px;border-radius:10px;background:#e5ece5;overflow:hidden;margin:12px 0}.progress-fill{height:100%;background:var(--accent);transition:width .25s}.stats{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:15px}.stat{border:1px solid var(--line);border-radius:13px;padding:15px;background:#fff}.stat b{display:block;font-size:26px;color:var(--navy)}.stat span{font-size:11px;color:var(--muted)}.card-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px}.choice{width:100%;display:block;text-align:left;background:#fff;border:1px solid #b9ccc2;color:var(--navy);border-radius:12px;padding:14px 17px;margin:10px 0;font-size:16px;min-height:50px}.choice:hover{border-color:var(--accent);background:var(--soft)}.choice.correct{border:2px solid var(--success);background:#e8f4e9}.choice.chosen{border:2px solid var(--accent);background:var(--soft)}.story{font-size:18px;line-height:1.8;max-width:780px}.story mark{background:#fff0b0;padding:1px 5px;border-radius:4px}.step-label{font-size:11px;font-weight:800;letter-spacing:1.1px;color:var(--accent);margin:18px 0 9px;text-transform:uppercase}.empty{border:1px dashed #b3c7bd;border-radius:14px;padding:25px;text-align:center;color:var(--muted)}.checklist{list-style:none;padding:0;margin:20px 0}.checklist li{padding:13px 0;border-bottom:1px solid var(--line);display:flex;gap:12px;align-items:center}.checklist .tag{margin-left:auto;font-size:11px;padding:4px 9px;border-radius:15px;background:#eaf0e9;white-space:nowrap}.lab-footer{display:flex;justify-content:space-between;gap:20px;border-top:1px solid var(--line);padding:21px 0;font-size:11px;color:var(--muted)}.reset-dialog{border:1px solid var(--line);border-radius:20px;padding:30px;color:var(--navy);max-width:min(90vw,470px)}.reset-dialog::backdrop{background:#092e4366}.visually-hidden{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.count{font-size:11px;color:var(--muted)}
/* Diagrams are built in code so lengths, fractions and labels agree. */
.diagram{overflow-x:auto;border:1px solid var(--line);border-radius:14px;background:#fafcf9;padding:20px;margin:20px 0}.diagram svg{display:block;max-width:100%;height:auto;margin:auto;min-width:300px}.diagram text{font-family:Lab,"Trebuchet MS",Arial,sans-serif;fill:var(--navy);font-size:24px}.diagram .diagram-small{font-size:19px;fill:var(--muted)}.model-label{font-size:12px;font-weight:700;color:var(--muted);margin-bottom:9px}.slider-row{display:grid;grid-template-columns:110px minmax(120px,1fr) 60px;gap:15px;align-items:center;margin:17px 0}.slider-row label{font-size:13px}.slider-value{font-weight:700;color:var(--accent);text-align:right}.comparison{display:grid;grid-template-columns:1fr 1fr;gap:18px}.model-key{display:flex;gap:18px;flex-wrap:wrap;color:var(--muted);font-size:11px;margin-top:12px}.model-key span::before{content:"";display:inline-block;width:11px;height:11px;border-radius:3px;margin-right:5px;background:var(--key,#347b81)}.fraction-inline{display:inline-flex;flex-direction:column;vertical-align:middle;text-align:center;font-variant-numeric:tabular-nums;line-height:1.1;margin:0 .18em;font-size:.85em}.fraction-inline .num{border-bottom:1.5px solid currentColor;padding:0 4px 3px}.fraction-inline .den{padding:3px 4px 0}.fraction-strip{display:flex;height:64px;border:1px solid #aec3b8;border-radius:9px;overflow:hidden;margin:12px 0 7px}.fraction-segment{display:flex;align-items:center;justify-content:center;text-align:center;font-size:12px;font-weight:700;min-width:0;border-right:1px solid #fff9;color:#123b47;transition:width .4s}.fraction-segment:last-child{border-right:0}.fraction-segment.first{background:#efbfa7}.fraction-segment.second{background:#b8cedc}.fraction-segment.left{background:#b3d8b9}.model-stage{padding:20px;border:1px solid var(--line);border-radius:13px;margin:14px 0}.fraction-form{display:flex;flex-wrap:wrap;gap:7px;align-items:center;font-weight:700}.fraction-form input{width:85px}.fraction-form .slash{font-size:24px}.reveal-lines{padding:0;list-style:none;margin:15px 0}.reveal-lines li{padding:12px 0;border-bottom:1px dashed var(--line);font-size:17px}.reveal-lines li:last-child{border:0}.rounds{display:flex;gap:7px;flex-wrap:wrap;margin-bottom:18px}.round{width:34px;height:34px;border-radius:50%;border:1px solid #bbcec1;background:#fff;font-size:12px;font-weight:700;color:var(--navy)}.round.active{background:var(--navy);color:#fff}.round.done{background:#d9eddc;border-color:#8bb696}.round.review{background:#fff0d7;border-color:#e6b760}.notice{font-size:12px;padding:10px 15px;border-left:3px solid var(--accent);background:var(--soft);color:var(--navy);border-radius:0 8px 8px 0}.svg-step{stroke:#fff;stroke-width:2}
@media(max-width:950px){.workspace{grid-template-columns:minmax(0,1fr) 240px}.panel{padding:22px}.card-grid{grid-template-columns:1fr 1fr}.studio-badge{display:none}.token{font-size:24px}.operation{width:38px;min-height:42px;font-size:24px}.expression{gap:5px}}
@media(max-width:720px){.lab-header,.lab-main,.lab-footer{width:calc(100% - 28px)}.lab-header{min-height:74px;gap:12px}.brand img{width:127px}.back-link{font-size:11px}.icon-button{padding:8px 10px;font-size:22px}.lab-main{padding-top:25px}.title-row{margin-bottom:20px}h1{letter-spacing:-1px}.subtitle{font-size:14px}.tabs{width:100%;gap:2px}.tab{flex:1;padding:11px 10px;font-size:12px}.workspace{grid-template-columns:1fr}.workspace>aside{order:2}.panel{padding:19px;border-radius:16px}.panel-heading{gap:10px}.panel-heading h2{font-size:21px}.expression{padding:19px 7px;gap:5px;min-height:110px}.token{font-size:21px}.operation{width:36px;min-height:40px;font-size:24px}.working{font-size:17px}.working small{width:100%;margin-left:24px}.comparison,.card-grid{grid-template-columns:1fr}.story{font-size:16px}.button{padding:11px 14px;font-size:13px}.lab-footer{font-size:10px}.lab-footer span:last-child{max-width:130px;text-align:right}.slider-row{grid-template-columns:90px 1fr 48px;gap:9px}.diagram{padding:12px}.answer-row{gap:10px}.answer-row label{min-width:130px}.fraction-form input{width:70px}}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{transition:none!important;scroll-behavior:auto!important}}

@media(max-width:720px){.diagram svg{min-width:0;width:100%}.diagram text{font-size:36px}.diagram .diagram-small{font-size:30px}}