:root{--navy-900: #071d42;--navy-800: #0b2a5b;--navy-700: #12407f;--blue-500: #1a73c9;--blue-300: #6fb8f2;--blue-100: #e3f1fd;--bg: #f4f7fb;--surface: #ffffff;--surface-2: #eef3f9;--text: #15203a;--muted: #4e5a73;--border: #c9d4e3;--focus: #ffb000;--ok: #1b6e3a;--ok-bg: #e6f4ea;--bad: #a3151c;--bad-bg: #fdecec;--warn: #7a4b00;--warn-bg: #fff4dc;--node-red: #c62828;--node-black: #1f2328;--nil: #3b4250;--highlight: #ffb000;--path: #1a73c9;--radius: 10px;--shadow: 0 1px 2px rgb(7 29 66 / 8%), 0 4px 14px rgb(7 29 66 / 8%);--font: "Segoe UI", system-ui, -apple-system, Roboto, "Helvetica Neue", Arial, sans-serif;--mono: ui-monospace, "Cascadia Mono", Consolas, monospace;color-scheme:light}*,*:before,*:after{box-sizing:border-box}html{-webkit-text-size-adjust:100%}body{margin:0;font-family:var(--font);font-size:1rem;line-height:1.55;color:var(--text);background:var(--bg)}img{max-width:100%}h1,h2,h3,h4{line-height:1.25;color:var(--navy-800);margin:0 0 .5em}h1{font-size:clamp(1.6rem,3.2vw,2.2rem)}h2{font-size:clamp(1.3rem,2.4vw,1.6rem)}h3{font-size:1.15rem}p{margin:0 0 .85em}a{color:var(--blue-500)}:focus-visible{outline:3px solid var(--focus);outline-offset:2px}.sr-only{position:absolute!important;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.skip-link{position:absolute;left:8px;top:-48px;z-index:100;background:var(--navy-800);color:#fff;padding:8px 14px;border-radius:6px}.skip-link:focus{top:8px}.container{width:min(1180px,100% - 32px);margin-inline:auto}main{padding:24px 0 48px}main:focus{outline:none}.site-header{background:var(--navy-800);color:#fff;border-bottom:4px solid var(--blue-300)}.site-header .bar{display:flex;align-items:center;gap:16px;padding:10px 0;flex-wrap:wrap}.brand{display:flex;align-items:center;gap:12px;color:#fff;text-decoration:none;margin-right:auto}.brand img.logo-small{width:56px;height:56px;object-fit:contain;border-radius:50%;background:#fff}.brand-title{font-weight:700;font-size:1.15rem;line-height:1.2}.brand-sub{display:block;font-weight:400;font-size:.85rem;color:var(--blue-100)}.student-chip{display:flex;align-items:center;gap:8px;font-size:.9rem;color:var(--blue-100)}.student-chip strong{color:#fff}.student-chip a{color:var(--blue-300)}.main-nav{background:var(--navy-900)}.main-nav ul{display:flex;flex-wrap:wrap;gap:2px;list-style:none;margin:0;padding:0}.main-nav a{display:block;padding:10px 14px;color:#dbe8f8;text-decoration:none;font-size:.95rem;border-bottom:3px solid transparent}.main-nav a:hover{color:#fff;background:#ffffff0f}.main-nav a.active,.main-nav a[aria-current=page]{color:#fff;font-weight:600;border-bottom-color:var(--blue-300)}.btn.nav-toggle{display:none}@media(max-width:760px){.btn.nav-toggle{display:inline-flex}.main-nav ul{flex-direction:column}.main-nav[data-open=false] ul,.brand-sub{display:none}}.site-footer{border-top:1px solid var(--border);padding:18px 0 28px;color:var(--muted);font-size:.9rem}.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:20px;box-shadow:var(--shadow)}.card+.card{margin-top:18px}.grid>.card+.card,.stack>.card+.card{margin-top:0}.grid>*{min-width:0}.grid{display:grid;gap:18px}.grid.cols-2{grid-template-columns:repeat(auto-fit,minmax(min(100%,420px),1fr))}.grid.cols-3{grid-template-columns:repeat(auto-fit,minmax(min(100%,300px),1fr))}.stack>*+*{margin-top:14px}.row{display:flex;flex-wrap:wrap;gap:10px;align-items:center}.spacer{flex:1}.muted{color:var(--muted)}.small{font-size:.9rem}.badge{display:inline-block;padding:2px 10px;border-radius:999px;font-size:.8rem;font-weight:600;border:1px solid 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var(--navy-700);background:var(--surface);color:var(--navy-800);font:inherit;font-weight:600;cursor:pointer;text-decoration:none;line-height:1.2}.btn:hover:not(:disabled){background:var(--blue-100)}.btn.primary{background:var(--navy-700);color:#fff}.btn.primary:hover:not(:disabled){background:var(--navy-800)}.btn.danger{border-color:var(--bad);color:var(--bad)}.btn.danger:hover:not(:disabled){background:var(--bad-bg)}.btn.ghost{border-color:transparent;background:transparent}.btn:disabled{opacity:.5;cursor:not-allowed}.btn[aria-pressed=true]{background:var(--navy-700);color:#fff}.site-header .btn{border-color:var(--blue-300);background:transparent;color:#fff}label{font-weight:600}.field-label{display:block}input[type=text],input[type=number],select{font:inherit;padding:9px 12px;border:1px solid #8796ad;border-radius:8px;background:#fff;color:var(--text);min-height:42px}input[type=number]{width:6.5em}input[aria-invalid=true]{border-color:var(--bad);box-shadow:0 0 0 1px var(--bad)}fieldset{border:1px solid var(--border);border-radius:var(--radius);padding:14px 16px;margin:0}legend{font-weight:700;color:var(--navy-800);padding:0 6px}.choice-list{display:grid;gap:8px}.choice{display:flex;gap:10px;align-items:flex-start;padding:10px 12px;border:1px solid var(--border);border-radius:8px;background:#fff;font-weight:400;cursor:pointer}.choice:hover{border-color:var(--blue-500)}.choice input{margin-top:4px;flex:none;width:18px;height:18px}.choice.correct{border-color:var(--ok);background:var(--ok-bg)}.choice.incorrect{border-color:var(--bad);background:var(--bad-bg)}.feedback{border-radius:8px;padding:12px 14px;border-left:5px solid}.feedback p:last-child{margin-bottom:0}.feedback.ok{background:var(--ok-bg);border-color:var(--ok)}.feedback.bad{background:var(--bad-bg);border-color:var(--bad)}.feedback.info{background:var(--blue-100);border-color:var(--blue-500)}.feedback.warn{background:var(--warn-bg);border-color:#d39a1a}.feedback-title{font-weight:700;margin-bottom:4px}.hero{display:flex;align-items:center;gap:28px;flex-wrap:wrap;background:linear-gradient(135deg,var(--navy-800),var(--navy-700));color:#fff;border-radius:14px;padding:24px;margin-bottom:24px}.hero h1,.hero h2{color:#fff}.hero p{color:#dbe8f8}.logo-large{width:clamp(180px,30vw,300px);height:auto;aspect-ratio:1 / 1;object-fit:contain;flex:none}.hero-text{flex:1 1 320px}.welcome{max-width:720px;margin:24px auto;text-align:center}.welcome .logo-large{width:clamp(220px,50vw,360px);margin:0 auto 12px;display:block}.welcome form{text-align:left}.activity-card{display:flex;flex-direction:column;gap:8px}.activity-card h3{margin:0}.activity-card .actions{margin-top:auto}.stat{display:flex;flex-direction:column}.stat .value{font-size:2rem;font-weight:700;color:var(--navy-800);line-height:1.1}.activity-header{margin-bottom:14px}.tabs{display:flex;gap:4px;border-bottom:2px solid var(--border);margin-bottom:18px;flex-wrap:wrap}.tab{font:inherit;font-weight:600;padding:10px 16px;border:1px solid transparent;border-bottom:none;border-radius:8px 8px 0 0;background:transparent;color:var(--muted);cursor:pointer;margin-bottom:-2px}.tab[aria-selected=true]{background:var(--surface);color:var(--navy-800);border-color:var(--border);border-bottom:2px solid var(--surface)}.tab .badge{margin-left:6px}.pager{display:flex;justify-content:space-between;gap:12px;margin-top:28px;flex-wrap:wrap}.step-counter{font-weight:600;color:var(--muted)}.toolbar{display:flex;flex-wrap:wrap;gap:8px;align-items:center;padding:10px;background:var(--surface-2);border:1px solid var(--border);border-radius:8px}.toolbar .sep{width:1px;align-self:stretch;background:var(--border)}.value-chip{display:inline-flex;align-items:center;justify-content:center;width:52px;height:52px;border-radius:50%;background:var(--node-red);color:#fff;font-weight:700;font-size:1.1rem;cursor:grab;border:3px solid #fff;box-shadow:0 0 0 2px var(--node-red)}.sequence{display:flex;gap:6px;flex-wrap:wrap;list-style:none;padding:0;margin:0}.sequence li{min-width:40px;padding:4px 8px;text-align:center;border-radius:6px;border:1px solid var(--border);background:#fff;font-weight:600}.sequence li.done{background:var(--ok-bg);border-color:#a8d5b5;color:var(--ok)}.sequence li.current{background:var(--warn-bg);border-color:#d39a1a}.score-box{display:flex;gap:18px;flex-wrap:wrap;align-items:baseline}.score-box 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.empty-text{fill:var(--muted);font-size:14px;text-anchor:middle}.legend{display:flex;flex-wrap:wrap;gap:14px;font-size:.85rem;color:var(--muted);padding:4px 6px}.legend span:before{content:"";display:inline-block;width:12px;height:12px;border-radius:50%;margin-right:5px;vertical-align:-1px}.legend .lg-red:before{background:var(--node-red)}.legend .lg-black:before{background:var(--node-black)}.legend .lg-nil:before{background:var(--nil);border-radius:2px}@media(prefers-reduced-motion:reduce){.tree-svg .node,.tree-svg .nil,.tree-svg .edge{transition:none}}.welcome input[type=text]{width:100%}@media print{@page{margin:16mm 14mm}body{background:#fff;color:#000;font-size:11pt}.site-header,.main-nav,.site-footer,.skip-link,.no-print,button,.btn{display:none!important}.print-only{display:block!important}main{padding:0}.container{width:100%}.card{box-shadow:none;border:none;padding:0}.print-header{display:flex!important;align-items:center;gap:14px;border-bottom:2px solid #000;padding-bottom:8px;margin-bottom:14px}.print-header img{width:64px;height:64px;object-fit:contain}table.report th,table.report td{border:1px solid #555}table.report th{background:#eee!important;-webkit-print-color-adjust:exact;print-color-adjust:exact}.report-block{break-inside:avoid}.badge{border:1px solid #555!important;background:#fff!important;color:#000!important}a{color:#000;text-decoration:none}}