:root{color-scheme:light;--ink:#1c2c3e;--sub:#5a6e82;--blue:#087bc4;--soft:#eaf5fd;--line:#dce7f0;--paper:#fff;--bg:#f4f8fc;--electron:#167bbb;--orange:#be5e24;--good:#14684b;--bad:#a03f2a}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.6 'NanumSquare',-apple-system,BlinkMacSystemFont,'Segoe UI','Malgun Gothic',sans-serif}button,select,input{font:inherit}button{cursor:pointer;border:1px solid var(--line);background:#fff;color:var(--ink);padding:10px 15px;min-height:44px;border-radius:10px;line-height:1.4}button:hover{background:var(--soft)}button:disabled{opacity:.45;cursor:default}button:focus-visible,select:focus-visible,input:focus-visible,summary:focus-visible{outline:3px solid #80c7f4;outline-offset:3px}.primary{background:var(--blue);color:#fff;border-color:var(--blue)}.primary:hover{background:#066daE}.quiet{background:transparent}header{background:#fff;border-bottom:1px solid var(--line)}.header-inner{max-width:1160px;margin:auto;display:flex;align-items:center;justify-content:space-between;padding:19px 28px;gap:16px}.brand{font-size:17px;font-weight:750;letter-spacing:1px}.breadcrumb{font-size:12px;color:var(--sub)}.badge{display:inline-block;color:var(--blue);background:var(--soft);border-radius:6px;padding:3px 8px;font-size:12px}.layout{max-width:1160px;margin:24px auto;display:grid;grid-template-columns:235px minmax(0,1fr);gap:24px;padding:0 24px}.sidebar{align-self:start;background:#fff;border:1px solid var(--line);border-radius:15px;padding:18px 12px}.sidebar h2{font-size:14px;margin:0 10px 6px}.global-progress{font-size:12px;color:var(--sub);margin:0 10px 12px}.navgroup{font-size:11px;font-weight:700;letter-spacing:1px;color:var(--sub);padding:17px 10px 5px}.nav-item{width:100%;display:flex;text-align:left;align-items:center;gap:10px;background:transparent;border:0;padding:9px 10px;border-radius:8px;font-size:13px;min-height:43px}.nav-item[aria-current=true]{background:var(--soft);color:#075e9d;font-weight:650}.nav-item .num{font-size:11px;min-width:21px;color:var(--sub)}.nav-item .check{margin-left:auto;color:var(--good)}main{min-width:0}.lesson{background:#fff;border:1px solid var(--line);border-radius:18px;overflow:hidden}.lesson-head{padding:24px 28px 20px;border-bottom:1px solid var(--line)}.lesson-head h1{font-size:26px;line-height:1.35;margin:8px 0 4px}.lesson-head p{font-size:14px;color:var(--sub);margin:0}.mobile-nav{display:none}.body{padding:24px 28px}.step-meta{display:flex;justify-content:space-between;gap:12px;font-size:12px;color:var(--sub);margin-bottom:8px}.progress{height:4px;background:#eef3f7;border-radius:8px;overflow:hidden;margin-bottom:21px}.progress i{display:block;height:100%;background:var(--blue);transition:width .25s}.step-title{font-size:21px;line-height:1.5;margin:0 0 8px;letter-spacing:-.4px}.explain{font-size:17px;line-height:1.8;margin:0;min-height:58px;word-break:keep-all}.stage{background:linear-gradient(180deg,#f7fbff,#f2f8fc);border-radius:14px;margin:20px 0 12px;padding:10px 10px 4px;position:relative}.stage svg{width:100%;height:auto;max-height:340px;display:block;overflow:visible}.legend{display:flex;justify-content:center;flex-wrap:wrap;gap:8px 18px;font-size:12px;color:var(--sub);min-height:28px;padding:0 0 9px}.legend i{display:inline-block;width:9px;height:9px;border-radius:50%;margin-right:5px;background:var(--electron)}.legend i.other{background:var(--orange)}.note{font-size:13px;color:var(--sub);line-height:1.7;margin:12px 0 18px;min-height:45px}.counts{display:flex;justify-content:center;gap:16px;flex-wrap:wrap;min-height:26px;font-size:14px;font-weight:600;padding:0 0 10px}.controls{display:flex;gap:8px;align-items:center;flex-wrap:wrap}.controls #next{margin-left:auto}.small-controls{display:flex;align-items:center;justify-content:space-between;gap:10px;margin-top:16px;padding-top:15px;border-top:1px solid var(--line);font-size:12px;color:var(--sub)}.small-controls button{font-size:12px;padding:6px 10px;min-height:36px}.speed{display:flex;align-items:center;gap:8px}.speed select{padding:5px 7px;border:1px solid var(--line);border-radius:6px;background:#fff;color:var(--ink)}.exercise{background:var(--soft);border-radius:12px;padding:18px;margin:16px 0}.exercise h3{font-size:16px;margin:0 0 9px}.exercise p{font-size:14px;margin:8px 0}.answers{display:flex;flex-wrap:wrap;gap:8px;margin-top:12px}.answers button{flex:1;min-width:70px}.feedback{min-height:25px;margin-top:12px!important;color:var(--ink)}.feedback.correct{color:var(--good)}.feedback.error{color:var(--bad)}.buildrows{display:flex;flex-direction:column;gap:8px}.buildrow{display:flex;justify-content:space-between;align-items:center;gap:12px;border-bottom:1px solid #cfdfed;padding:6px 0}.buildrow:last-child{border:0}.buildrow label{font-size:14px}.buildrow select{border:1px solid #bfd3e5;border-radius:7px;padding:7px;background:#fff;max-width:150px;min-height:40px}.builder-actions{display:flex;gap:8px;flex-wrap:wrap;margin-top:14px}.completion{text-align:center;padding:20px}.completion h2{font-size:24px}.completion p{color:var(--sub);font-size:15px}.ref{background:#fff;border:1px solid var(--line);border-radius:12px;margin-top:20px;padding:16px 20px}.ref summary{font-size:14px;font-weight:600;cursor:pointer}.table-wrap{overflow:auto;margin-top:12px}table{border-collapse:collapse;width:100%;font-size:13px}th,td{padding:10px 7px;text-align:left;border-bottom:1px solid var(--line)}th{font-weight:600;background:var(--bg)}td.num{text-align:center}footer{max-width:1160px;margin:20px auto 35px;padding:0 24px;color:var(--sub);font-size:12px}.offline-alert{background:#fff1da;padding:9px 15px;font-size:13px}.hidden,[hidden]{display:none!important}math{font-family:'Cambria Math','STIX Two Math',serif;font-size:1.08em}.mini-stats{font-size:12px;color:var(--sub);margin-top:8px}.modebar{display:flex;gap:8px;flex-wrap:wrap;margin-top:14px}.modebar button{font-size:12px;min-height:36px;padding:7px 10px}.reduced{font-size:12px;color:var(--sub)}
@media(max-width:800px){.layout{grid-template-columns:1fr;margin:16px auto;padding:0 14px}.sidebar{display:none}.header-inner{padding:15px 18px}.mobile-nav{display:block;margin-bottom:12px}.mobile-nav label{display:block;font-size:12px;color:var(--sub);margin:0 0 5px}.mobile-nav select{width:100%;padding:12px;border:1px solid var(--line);border-radius:10px;background:#fff;font-size:15px}.lesson-head{padding:20px}.body{padding:20px}.stage svg{max-height:320px}}
@media(max-width:420px){.layout{padding:0 9px}.header-inner{padding:13px 14px}.brand{font-size:14px}.header-inner>.badge{display:none}.lesson-head{padding:18px 16px}.lesson-head h1{font-size:22px}.body{padding:17px 14px}.step-title{font-size:19px}.explain{font-size:16px;min-height:85px}.stage{padding:5px 0}.controls{gap:6px}.controls button{font-size:13px;padding:9px 10px}.small-controls{align-items:flex-start;flex-wrap:wrap}.buildrow{align-items:flex-start}.ref{padding:14px}th,td{font-size:12px}.exercise{padding:14px}.legend{font-size:11px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important}.progress i{transition:none}}
@media print{header,.sidebar,.mobile-nav,.lesson,.controls,footer{display:none}.layout{display:block}.ref{border:0}.ref summary{display:none}.ref>*{display:block!important}body{background:#fff}}

.site-return{display:block;color:var(--blue);text-decoration:none;font-size:13px;min-height:44px;padding:10px 0;margin-top:4px}.site-return:focus-visible{outline:2px solid var(--blue);outline-offset:3px}.brand{color:var(--blue);font-size:15px;letter-spacing:.06em}@media(max-width:420px){.brand{font-size:13px;letter-spacing:.035em}}