:root{font:20px/1.45 'Microsoft YaHei','PingFang SC',system-ui,sans-serif;color:#111d3a;background:#101d43;--blue:#174bd1;--orange:#c74806;--navy:#101d43;--ink:#111d3a;--line:#cbd6ed;--white:#fff;font-synthesis:none}
*{box-sizing:border-box}body{margin:0}button,input,select{font:inherit}button{cursor:pointer;touch-action:manipulation;user-select:none}button,a,input,select{-webkit-tap-highlight-color:transparent}button{border:2px solid #becce5;background:white;color:var(--ink);min-height:48px;padding:9px 17px;border-radius:10px;font-weight:750}button:hover:not(:disabled){border-color:var(--blue);background:#f0f5ff}button:active:not(:disabled){transform:translateY(2px)}button:disabled{cursor:default}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible{outline:4px solid #ffbb00;outline-offset:3px}.primary{background:var(--blue);border-color:var(--blue);color:#fff}.primary:hover:not(:disabled){background:#113ba8;color:#fff}.quiet{background:transparent;border-color:transparent;padding:7px 12px;min-height:44px}.topbar .quiet{color:white}.topbar .quiet:hover:not(:disabled){background:#ffffff16;border-color:#ffffff70}.app-shell{max-width:none;margin:auto;padding:0 14px;min-height:100dvh;display:flex;flex-direction:column}.topbar{height:64px;flex:none;display:flex;justify-content:space-between;align-items:center;gap:18px;color:white}.brand{display:flex;align-items:center;gap:10px;color:white;text-decoration:none;font-weight:900;font-size:1.25rem;white-space:nowrap}.brand-icon{width:38px;height:38px;background:#fff;color:var(--blue);border-radius:9px;display:grid;place-items:center}.brand small{display:inline;font-size:.72rem;font-weight:600;margin-left:10px;color:#d2e1ff}.topbar nav{display:flex;gap:4px}.topbar button{font-size:.8rem}#main{min-width:0;flex:1}.site-footer{color:#d4e0ff;font-size:.65rem;display:flex;justify-content:space-between;align-items:center;gap:10px;padding:11px 0}.version{margin-left:12px}.home{max-width:1350px;margin:18px auto 30px;background:#fff;border-radius:20px;padding:28px 32px}.home-title{display:flex;align-items:end;justify-content:space-between;gap:24px;border-bottom:3px solid #153879;padding-bottom:20px}.home h1{font-size:2.7rem;letter-spacing:-.04em;margin:0;line-height:1.2}.home h1 span{color:var(--blue)}.home-title p{margin:0 0 2px;font-size:1rem;font-weight:700;line-height:1.7}.home-title b{color:var(--orange)}.section-title{font-size:1rem;margin:22px 0 12px}.category-grid{display:grid;grid-template-columns:1.15fr repeat(4,1fr);gap:10px}.category{min-height:85px;text-align:left;padding:14px;background:#f5f8ff;border-color:#d0dcf5}.category strong{display:block;font-size:1.13rem}.category small{display:block;font-size:.7rem;font-weight:500;color:#344e7f;margin-top:6px}.category.selected{background:var(--blue);border-color:var(--blue);color:white}.category.selected small{color:white}.settings-row{display:flex;align-items:end;gap:30px;margin:24px 0;flex-wrap:wrap}.field{display:grid;gap:8px}.field>span{font-size:.85rem;font-weight:800}.segments{display:flex;gap:6px}.segments button{font-size:.88rem;min-height:44px;padding:7px 12px}.segments .selected{border-color:var(--blue);background:#e8efff;color:#123dae}.segments button:disabled{opacity:.4}.names{display:flex;gap:12px}.names label{font-size:.8rem;font-weight:800;display:grid;gap:7px}.names input{width:155px;border:2px solid #c1d0ef;border-radius:8px;padding:8px 10px;background:white}.names label:last-child input{border-color:#e1ae91}.team0{color:var(--blue)}.team1{color:var(--orange)}.home-actions{display:flex;gap:12px;align-items:center;flex-wrap:wrap}.launch{font-size:1.35rem;min-height:62px;min-width:340px;margin-left:auto}.home-rule{display:flex;justify-content:space-between;gap:15px;flex-wrap:wrap;background:#eff4ff;border-radius:10px;padding:14px 16px;font-size:.85rem;font-weight:700}.home-rule span:last-child{color:#374d73}.home-bottom{display:flex;justify-content:space-between;align-items:center;margin-top:15px;gap:12px}.subtle{color:#40547b;font-size:.85rem;line-height:1.8}.pill{display:inline-flex;align-items:center;font-size:.7rem;line-height:1.4;padding:5px 9px;border:1px solid #becdec;border-radius:7px;color:#294e9a;background:#edf3ff;font-weight:700}kbd{font:700 .76rem system-ui;border:1px solid #b6c4df;border-bottom-width:3px;background:white;border-radius:5px;padding:3px 7px;color:#153c86}
/* The bottom answer dock is a flex sibling of the flexible observation stage. */
body.in-race .app-shell{height:100dvh;min-height:0}body.in-race .topbar{height:54px}body.in-race .site-footer{display:none}body.in-race #main{min-height:0;display:flex;flex-direction:column;padding-bottom:12px}.race{height:100%;min-height:0;display:flex;flex-direction:column;position:relative;gap:8px}.race-toolbar{display:flex;justify-content:space-between;align-items:center;gap:12px;min-height:42px;flex:none;color:white}.race-toolbar h1{margin:0;font-size:.95rem;font-weight:700}.race-toolbar>div{display:flex;gap:8px;align-items:center}.race-toolbar button{font-size:.8rem;min-height:38px;padding:5px 12px;border-color:#9caed0}.race-toolbar .demo-flag{color:#ffdd59}.race-arena{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:14px;flex:1;min-height:0}.race-lane{--team:var(--blue);--wash:#edf3ff;display:flex;flex-direction:column;min-width:0;min-height:0;background:#fff;border:3px solid var(--team);border-radius:14px;overflow:hidden;position:relative}.race-lane.right{--team:var(--orange);--wash:#fff2e9}.lane-head{display:flex;align-items:center;justify-content:space-between;background:var(--team);color:#fff;padding:8px 14px;min-height:58px;gap:12px;flex:none}.lane-head h2{font-size:1.28rem;margin:0;font-weight:900;overflow-wrap:anywhere}.lane-head .score{font-size:1.8rem;font-weight:900;line-height:1}.lane-head .score small{font-size:.65rem;margin-left:5px}.lane-progress{font-size:.86rem;white-space:nowrap;font-weight:800}.lane-hud{display:flex;align-items:center;justify-content:space-between;gap:10px;padding:8px 16px 0;flex:none}.lane-hud .category-label{color:var(--team);font-size:.82rem;font-weight:850}.lane-clock{font-size:1.05rem;font-weight:900;font-variant-numeric:tabular-nums}.lane-clock.urgent{color:#b71924}.timer-track{height:4px;background:#e0e8f9;flex:none;margin:6px 16px 0;overflow:hidden}.timer-track i{display:block;height:100%;width:100%;background:var(--team)}.lane-study{flex:1;min-height:0;display:flex;flex-direction:column;padding:10px 15px 8px;gap:7px}.question-stem{font-size:clamp(1.4rem,2vw,2.15rem);font-weight:850;line-height:1.45;margin:0;flex:none;overflow-wrap:anywhere}.visual{min-height:110px;flex:1;display:flex;align-items:center;justify-content:center;position:relative;border:1px solid #d0dbef;background:#fff;border-radius:8px;overflow:hidden}.visual svg{width:100%;height:100%;min-height:0;display:block}.visual video{width:100%;height:100%;object-fit:contain;min-height:0;background:white;display:block}.visual .media-error{padding:15px;font-size:1rem;color:#a81c26}.media-controls{display:flex;justify-content:space-between;align-items:center;gap:10px;flex:none;min-height:28px}.media-controls span{font-size:.65rem;color:#405478}.media-controls button{font-size:.75rem;min-height:30px;border:1px solid #bacbe8;padding:3px 10px;border-radius:6px}.answer-dock{margin-top:auto;flex:none;padding:10px 12px 9px;background:var(--wash);border-top:3px solid var(--team)}.choices{display:grid;grid-template-columns:1fr 1fr;grid-auto-rows:minmax(106px,auto);gap:9px}.choice{font-size:clamp(1.2rem,1.65vw,1.8rem);line-height:1.35;font-weight:800;display:flex;align-items:center;gap:10px;text-align:left;min-width:0;padding:10px 12px;border:2px solid #a8bce7;border-bottom-width:5px;background:#fff;color:#101c38;min-height:106px;border-radius:9px;overflow-wrap:anywhere}.right .choice{border-color:#dca684}.choice:hover:not(:disabled){background:#e5eeff;border-color:#174bd1}.right .choice:hover:not(:disabled){background:#ffe3cf;border-color:#b84006}.choice:disabled{opacity:.6}.choice-code{display:flex;align-items:center;justify-content:center;width:34px;height:39px;background:var(--team);color:white;border-radius:6px;flex-shrink:0;font-size:1.05rem;font-weight:900}.choice-text{min-width:0}.lane-message{display:flex;align-items:center;justify-content:space-between;gap:10px;min-height:37px;font-size:.84rem;font-weight:800;color:#183d8b;padding-top:8px;line-height:1.4}.right .lane-message{color:#a73805}.lane-message .keys{font-size:.65rem;font-weight:600;white-space:nowrap}.race-lane.feedback .choice{opacity:.35}.race-lane.feedback .lane-message{font-size:1rem}.race-lane.feedback .lane-message.wrong{color:#b31c29}.race-lane.feedback .lane-message.good{color:#165db0}.feedback-flash{position:absolute;left:50%;top:52%;transform:translate(-50%,-50%);padding:14px 26px;background:#174bd1;color:white;font-size:1.5rem;font-weight:900;border-radius:12px;box-shadow:0 8px 30px #10265430;z-index:2;pointer-events:none;white-space:nowrap}.feedback-flash.wrong{background:#b51f2e}.finished-study{display:flex;align-items:center;justify-content:center;flex:1;flex-direction:column;text-align:center;padding:20px;color:var(--team);gap:14px}.finished-study strong{font-size:2.2rem}.finished-study p{font-size:1.1rem;margin:0}.finished-study .finish-score{font-size:4rem;font-weight:900}.finished-study small{font-size:.85rem;color:#304773}.race-lane.finished .choice{visibility:hidden}.race-lane.finished .answer-dock{border-top:0;background:white}.race-lane.finished .lane-message{color:var(--team);justify-content:center;font-size:1rem}.screen-overlay{position:absolute;inset:0;z-index:5;background:#101d43ed;display:flex;align-items:center;justify-content:center;text-align:center;color:white;border-radius:12px;padding:24px}.screen-overlay h2{font-size:2.6rem;margin:0 0 15px}.screen-overlay p{font-size:1.1rem;line-height:1.8;margin:12px 0}.screen-overlay .count{font-size:6rem;line-height:1.2;font-weight:950;color:#ffdd59}.screen-overlay button{font-size:1.2rem;min-height:60px}.screen-overlay .count-label{font-size:1.6rem;font-weight:800}.paused .schematic-motion *{animation-play-state:paused!important}
.result{max-width:1350px;margin:20px auto 35px;background:white;padding:25px 30px;border-radius:16px}.result-title{text-align:center}.result-title h1{font-size:2.25rem;margin:12px 0}.result-title p{margin:0 0 18px}.scoreboard{display:grid;grid-template-columns:1fr 1fr;gap:18px}.result-team{padding:20px;border:3px solid var(--blue);border-radius:12px;background:#edf3ff}.result-team.right{border-color:var(--orange);background:#fff1e6}.result-team h2{font-size:1.25rem;margin:0 0 10px}.metrics{display:flex;align-items:center;justify-content:space-between;gap:15px}.metrics strong{font-size:2.6rem}.metrics small{font-size:.9rem}.metrics p{font-size:.9rem;line-height:1.8;margin:0}.type-scores{display:flex;flex-wrap:wrap;gap:8px;margin-top:13px}.type-scores span{padding:5px 8px;background:white;border-radius:5px;font-size:.77rem;font-weight:700}.result-actions{display:flex;justify-content:center;gap:10px;flex-wrap:wrap;margin:20px 0}.review-tools{display:flex;justify-content:space-between;align-items:center;gap:14px;margin:24px 0 12px}.review-tools h2{font-size:1.1rem;margin:0}.review-list{display:grid;gap:10px}.review-item{border:2px solid #d0dbef;border-radius:9px;padding:12px 16px}.review-item summary{font-size:1rem;line-height:1.7;font-weight:750;cursor:pointer}.review-item p{font-size:.9rem;line-height:1.85;margin:10px 0}.review-result{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px}.badge{font-size:.8rem;background:#e4edff;color:#174194;padding:5px 8px;border-radius:5px}.badge.bad{background:#ffe3df;color:#9d1c23}.source-copy{font-size:.9rem;line-height:1.9}.source-copy a{color:#143fb1;overflow-wrap:anywhere}.source-copy li{margin:8px 0}dialog{border:3px solid #1b4094;border-radius:15px;color:var(--ink);background:white;padding:28px;max-width:min(1100px,94vw);min-width:min(560px,94vw);max-height:89dvh;box-shadow:0 20px 100px #050d2b66}dialog::backdrop{background:#07102dbb}.dialog-close{position:absolute;right:8px;top:6px;font-size:1rem}.dialog-heading{padding-right:35px}.dialog-heading h2{font-size:1.55rem;margin:0 0 10px}.dialog-heading p{font-size:.9rem;line-height:1.8;margin:0 0 12px}.tool-tabs{display:flex;gap:10px;margin:15px 0}.tool-tabs .selected{background:var(--blue);color:white;border-color:var(--blue)}.teacher-jump{display:flex;gap:12px;align-items:end;margin-bottom:17px}.teacher-jump label{display:grid;flex:1;gap:8px;font-size:.85rem;font-weight:700}.teacher-jump select{min-width:0;padding:9px;border:2px solid #c1d1f1;border-radius:8px;background:white}.question-list{display:grid;gap:9px}.question-list button{display:flex;text-align:left;align-items:center;gap:12px;font-size:.83rem}.qid{font-size:.65rem;min-width:65px;color:#3c5786}.qstem{min-width:0}.media-library{display:grid;grid-template-columns:1fr 1fr;gap:14px}.media-item{border:2px solid #d0dbef;padding:12px;border-radius:9px}.media-item video{width:100%;height:220px;background:#fff;object-fit:contain}.media-item h3{font-size:1rem;margin:0 0 10px}.media-item p{font-size:.72rem;line-height:1.7}.demo-solution{padding:12px;background:#edf3ff;border-radius:8px;font-size:.85rem;line-height:1.8}.demo-solution strong{display:block}.demo-banner{background:#ffdf67;color:#352700;padding:6px 12px;font-size:.82rem;font-weight:800;border-radius:7px}#toast{position:fixed;bottom:20px;left:50%;transform:translateX(-50%);padding:12px 18px;border-radius:10px;background:#07132f;color:white;font-size:.85rem;opacity:0;z-index:30;pointer-events:none;max-width:92vw}#toast.shown{opacity:1}
/* Original schematic motion, unchanged teaching graphics. */
.schematic-motion .travel{animation:cross 3.5s infinite ease-in-out}.schematic-motion .water{animation:water-cross 3s infinite ease-in-out}.schematic-motion .cargo{animation:carrier 4s infinite ease-in-out}.schematic-motion .endocargo{animation:gulp 4s infinite ease-in-out}.schematic-motion .exocargo{animation:release 4s infinite ease-in-out}.schematic-motion .carrier-out{animation:open-out 4s infinite steps(1)}.schematic-motion .carrier-in{animation:open-in 4s infinite steps(1)}.schematic-motion .sequence{opacity:0;animation:sequence 6s infinite steps(1)}.schematic-motion .step-1{animation-delay:-4s}.schematic-motion .step-2{animation-delay:-2s}.schematic-motion.stopped *{animation-play-state:paused!important}.motion-reduced .schematic-motion *{animation:none!important}.motion-reduced .sequence.step-0{opacity:1}.motion-reduced .sequence.step-1,.motion-reduced .sequence.step-2,.motion-reduced .carrier-in{opacity:0}@keyframes cross{0%,10%{transform:translateY(-70px)}70%,100%{transform:translateY(85px)}}@keyframes carrier{0%,20%{transform:translateY(-50px)}70%,100%{transform:translateY(96px)}}@keyframes gulp{0%,20%{transform:translateY(-35px)}85%,100%{transform:translateY(118px)}}@keyframes release{0%,20%{transform:translateY(0)}85%,100%{transform:translateY(-150px)}}@keyframes water-cross{0%,10%{transform:translateX(-60px)}70%,100%{transform:translateX(62px)}}@keyframes open-out{0%,49%{opacity:1}50%,100%{opacity:0}}@keyframes open-in{0%,49%{opacity:0}50%,100%{opacity:1}}@keyframes sequence{0%,32%{opacity:1}33%,100%{opacity:0}}
@media(min-width:1700px) and (min-height:900px){.topbar{height:70px}.brand{font-size:1.5rem}.topbar button{font-size:1rem;min-height:48px}body.in-race .topbar{height:64px}.lane-head{min-height:75px;padding:10px 20px}.lane-head h2{font-size:1.65rem}.lane-progress{font-size:1.05rem}.lane-head .score{font-size:2.3rem}.lane-hud{padding:10px 20px 0}.lane-hud .category-label{font-size:1rem}.lane-clock{font-size:1.35rem}.lane-study{padding:13px 20px 10px;gap:10px}.answer-dock{padding:14px 18px 10px}.choices{grid-auto-rows:minmax(140px,auto);gap:12px}.choice{padding:12px 16px;min-height:140px}.choice-code{width:46px;height:50px;font-size:1.35rem}.lane-message{min-height:44px;font-size:1.05rem}.lane-message .keys{font-size:.8rem}.media-controls span{font-size:.8rem}.media-controls button{font-size:.9rem;min-height:37px}.race-toolbar h1{font-size:1.08rem}.race-toolbar button{font-size:1rem;min-height:44px}.home{margin:35px auto}.home h1{font-size:3.5rem}.home-title p{font-size:1.2rem}.category{min-height:110px}.category strong{font-size:1.4rem}.home-rule{font-size:1rem}}
@media(max-width:1100px){:root{font-size:18px}.app-shell{padding:0 9px}.topbar{height:58px}.topbar button{font-size:.78rem;padding:6px 8px}.brand small{display:none}.race-arena{gap:9px}.lane-head{padding:8px 10px}.lane-head h2{font-size:1.15rem}.lane-progress{font-size:.8rem}.lane-study{padding:9px 10px 7px}.question-stem{font-size:1.45rem}.choices{grid-auto-rows:minmax(108px,auto);gap:7px}.choice{font-size:1.2rem;padding:8px;gap:7px}.choice-code{width:27px;height:34px;font-size:.95rem}.answer-dock{padding:9px 8px}.home{padding:22px}.home-title{align-items:start}.home h1{font-size:2.2rem}.home-title p{font-size:.9rem}.category strong{font-size:1rem}.settings-row{gap:20px}.launch{min-width:260px}.brand{font-size:1.15rem}}
@media(max-height:700px) and (min-width:900px){body.in-race .topbar{height:45px}.race-toolbar{min-height:34px}.race-toolbar button{min-height:32px}.lane-head{min-height:48px;padding:5px 12px}.lane-hud{padding-top:5px}.lane-study{padding-top:7px}.question-stem{font-size:1.32rem}.choices{grid-auto-rows:minmax(90px,auto)}.choice{min-height:90px;font-size:1.1rem}.lane-message{min-height:32px;padding-top:5px}.answer-dock{padding:7px 9px}.visual{min-height:90px}}
@media(max-width:720px){:root{font-size:17px}.topbar{height:auto;padding:10px 0;gap:8px;flex-wrap:wrap}.topbar nav{width:100%;justify-content:space-between}.brand small{display:inline;font-size:.7rem}.topbar button{font-size:.8rem}.home{margin-top:8px;padding:18px 14px}.home-title{display:block}.home h1{font-size:2rem}.home-title p{margin-top:12px}.category-grid{grid-template-columns:1fr 1fr}.category:first-child{grid-column:1/-1}.category{min-height:75px}.settings-row{gap:16px}.names input{width:130px}.launch{width:100%;min-width:0;margin:0}.home-actions{margin-top:15px}.home-rule{font-size:.78rem}.home-bottom{flex-wrap:wrap}.race-toolbar{flex-wrap:wrap}.race-toolbar h1{font-size:.9rem}.race-toolbar>div{margin-left:auto}body.in-race .app-shell{height:auto;min-height:100dvh}body.in-race #main{min-height:0}body.in-race .topbar{height:auto}.race-arena{grid-template-columns:1fr 1fr;min-height:900px}.race-lane{min-height:900px}.lane-head{flex-wrap:wrap;gap:5px;padding:8px}.lane-head h2{font-size:1rem}.lane-head .score{font-size:1.4rem}.lane-progress{font-size:.7rem}.lane-hud{padding:7px 8px 0}.lane-clock{font-size:.9rem}.lane-hud .category-label{font-size:.7rem}.lane-study{padding:8px}.question-stem{font-size:1.1rem;line-height:1.5}.visual{min-height:140px}.media-controls{flex-wrap:wrap}.media-controls span{font-size:.55rem}.media-controls button{font-size:.65rem}.choices{grid-template-columns:1fr;grid-auto-rows:minmax(90px,auto);gap:7px}.choice{font-size:1rem;min-height:90px;padding:8px 6px;gap:6px}.choice-code{width:23px;height:30px;font-size:.8rem}.answer-dock{padding:8px 6px}.lane-message{font-size:.7rem;flex-wrap:wrap;justify-content:center;min-height:55px}.lane-message .keys{font-size:.6rem}.feedback-flash{font-size:1rem;padding:10px}.finished-study{padding:10px}.finished-study strong{font-size:1.3rem}.finished-study p{font-size:.85rem}.finished-study .finish-score{font-size:2.4rem}.result{padding:18px 13px}.result-title h1{font-size:1.65rem}.scoreboard{gap:9px}.result-team{padding:12px}.metrics{display:block}.metrics strong{font-size:2rem}.metrics p{font-size:.75rem}.result-team h2{font-size:1rem}.review-tools{flex-wrap:wrap}.media-library{grid-template-columns:1fr}.teacher-jump{flex-wrap:wrap}.teacher-jump button{width:100%}.tool-tabs button{font-size:.8rem}.question-list button{display:block}.question-list .qid{margin-right:8px}.qstem{display:block;margin-top:7px}dialog{padding:24px 15px}.screen-overlay{position:fixed;inset:20% 5%;z-index:10}.screen-overlay h2{font-size:2rem}.site-footer{font-size:.62rem}.question-list .pill{font-size:.6rem}.metrics small{font-size:.7rem}}
.lane-hud{padding:4px 15px 0;min-height:27px}.lane-hud .category-label{font-size:.7rem}.lane-head{min-height:52px}.lane-head .lane-clock{color:white;font-size:.9rem}.timer-track{margin-top:4px}.lane-study{padding-top:8px}.media-controls:has(span:only-child){min-height:18px}.media-controls:has(span:only-child) span{font-size:.64rem}
.large-type.in-race .app-shell{height:auto;min-height:100dvh}.large-type .race-arena{min-height:1100px}.large-type .race-lane{min-height:1100px}.large-type .lane-study{flex:none}.large-type .visual{min-height:240px;height:240px;flex:none}.large-type .choice{min-height:140px}.large-type .choices{grid-auto-rows:minmax(140px,auto)}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation:none!important;transition:none!important}}

/* Difficulty selection and explicit teaching motion controls. */
.category-grid{grid-template-columns:1fr 1fr}.category:first-child{grid-column:auto}.category strong{font-size:1.35rem}.category small{font-size:.9rem}.motion-actions{display:flex;gap:5px;flex-wrap:wrap}.motion-actions button{white-space:nowrap;min-height:34px}.media-controls>[data-motion-status]{max-width:48%;line-height:1.3}.media-item .media-controls{justify-content:flex-start;flex-wrap:wrap}.media-item svg{height:100%;width:100%}@media(max-width:720px){.category-grid{grid-template-columns:1fr}.media-controls>[data-motion-status]{max-width:100%}.motion-actions{gap:4px}.motion-actions button{font-size:.7rem}}