/* ===== 정처기 공부 — shared design system (mobile-first) ===== */
:root{
  --bg:#f5f6fb; --card:#ffffff; --ink:#1b2233; --muted:#5b6478;
  --line:#e4e7ef; --brand:#3b56d6; --brand-2:#6a3fd6; --brand-soft:#eef1fe;
  --key:#2563eb; --key-bg:#eff6ff; --tip:#0f9d6a; --tip-bg:#ecfdf5;
  --warn:#d9772b; --warn-bg:#fff7ed; --exam:#8b3fd6; --exam-bg:#f7f0ff;
  --code:#eef1f6; --shadow:0 1px 3px rgba(20,30,60,.06),0 8px 24px rgba(20,30,60,.05);
}
@media (prefers-color-scheme: dark){
  :root{
    --bg:#0f131c; --card:#171c28; --ink:#e6e9f2; --muted:#9aa3b8;
    --line:#28303f; --brand:#7d93ff; --brand-soft:#1c2440;
    --key:#7db0ff; --key-bg:#132132; --tip:#57d6a4; --tip-bg:#0f2620;
    --warn:#e8a366; --warn-bg:#2a2013; --exam:#c39cf0; --exam-bg:#211735;
    --code:#222a38; --shadow:0 1px 3px rgba(0,0,0,.4);
  }
}
*{box-sizing:border-box}
html{scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{
  margin:0;background:var(--bg);color:var(--ink);
  font-family:"Pretendard","Apple SD Gothic Neo","Malgun Gothic",system-ui,sans-serif;
  line-height:1.7;font-size:16px;-webkit-font-smoothing:antialiased;
}

/* ---- top site bar (sticky, mobile-friendly) ---- */
header.site{position:sticky;top:0;z-index:50;background:var(--card);
  border-bottom:1px solid var(--line);box-shadow:var(--shadow)}
.bar{max-width:960px;margin:0 auto;display:flex;align-items:center;gap:8px;
  padding:10px 14px;flex-wrap:wrap}
.brand{font-weight:800;text-decoration:none;color:var(--ink);font-size:1.02rem;
  white-space:nowrap;letter-spacing:-.3px}
nav.top{display:flex;gap:4px;margin-left:auto;overflow-x:auto;
  -webkit-overflow-scrolling:touch}
nav.top a{text-decoration:none;color:var(--muted);font-weight:600;font-size:.9rem;
  padding:6px 11px;border-radius:9px;white-space:nowrap}
nav.top a:hover,nav.top a.on{background:var(--brand-soft);color:var(--brand)}

.wrap{max-width:840px;margin:0 auto;padding:20px 16px 60px}

/* ---- hero (home) ---- */
.hero{text-align:center;padding:30px 16px 12px}
.hero h1{font-size:1.7rem;margin:0 0 8px;letter-spacing:-.6px;
  background:linear-gradient(120deg,var(--brand),var(--brand-2));
  -webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}
.hero p{color:var(--muted);margin:0;font-size:.98rem}

/* ---- cards grid (home) ---- */
.cards{display:grid;grid-template-columns:1fr;gap:14px;margin-top:22px}
@media(min-width:620px){.cards{grid-template-columns:1fr 1fr}}
.card{display:block;text-decoration:none;color:inherit;background:var(--card);
  border:1px solid var(--line);border-radius:16px;padding:18px 20px;box-shadow:var(--shadow);
  transition:transform .12s ease,border-color .12s ease}
.card:hover{transform:translateY(-2px);border-color:var(--brand)}
.card .ic{font-size:1.6rem}
.card h3{margin:8px 0 4px;font-size:1.12rem}
.card p{margin:0;color:var(--muted);font-size:.9rem}
.card .badge{display:inline-block;margin-top:10px;font-size:.75rem;font-weight:700;
  padding:2px 9px;border-radius:20px}
.b-red{background:#fdecec;color:#c0392b} .b-org{background:#fff2e5;color:#a04000}
.b-blu{background:var(--key-bg);color:var(--key)}
@media (prefers-color-scheme: dark){.b-red{background:#3a1e1e;color:#f5a6a6}.b-org{background:#3a2a17;color:#f0c08a}}

/* ---- sections ---- */
section{background:var(--card);border:1px solid var(--line);border-radius:16px;
  padding:20px 18px;margin-bottom:18px;box-shadow:var(--shadow);scroll-margin-top:66px}
section>h2{margin:0 0 4px;font-size:1.25rem;display:flex;align-items:center;gap:10px;letter-spacing:-.3px}
.num{background:var(--brand);color:#fff;min-width:28px;height:28px;border-radius:8px;
  display:inline-flex;align-items:center;justify-content:center;font-size:.85rem;flex:0 0 auto}
.lead{color:var(--muted);margin:.2rem 0 1rem;font-size:.92rem}
h3{margin:20px 0 8px;font-size:1.04rem;border-left:4px solid var(--brand);padding-left:10px}
p{margin:.4rem 0}
ul,ol{margin:.4rem 0;padding-left:20px} li{margin:3px 0}

/* ---- in-page chip nav ---- */
.chipnav{display:flex;flex-wrap:wrap;gap:6px;margin:4px 0 18px}
.chipnav a{text-decoration:none;font-size:.83rem;font-weight:600;color:var(--brand);
  background:var(--brand-soft);border-radius:20px;padding:4px 11px}

/* ---- callout boxes ---- */
.box{border-radius:12px;padding:11px 15px;margin:12px 0;font-size:.92rem;border:1px solid}
.box .h{font-weight:700;font-size:.8rem;letter-spacing:.3px;display:block;margin-bottom:4px}
.key{background:var(--key-bg);border-color:#c9dcfb}  .key .h{color:var(--key)}
.tip{background:var(--tip-bg);border-color:#bfead6}   .tip .h{color:var(--tip)}
.warn{background:var(--warn-bg);border-color:#f6d5b0} .warn .h{color:var(--warn)}
.exam{background:var(--exam-bg);border-color:#e2ccf7} .exam .h{color:var(--exam)}
@media (prefers-color-scheme: dark){
  .key{border-color:#26456e}.tip{border-color:#1c4c3a}.warn{border-color:#4d3a1e}.exam{border-color:#3d2b58}
}

/* ---- tables (horizontal scroll on mobile) ---- */
.tw{overflow-x:auto;-webkit-overflow-scrolling:touch;margin:12px 0;
  border:1px solid var(--line);border-radius:10px}
table{width:100%;border-collapse:collapse;font-size:.88rem;min-width:460px}
th,td{border-bottom:1px solid var(--line);border-right:1px solid var(--line);
  padding:8px 11px;text-align:left;vertical-align:top}
th{background:var(--brand-soft);font-weight:700;color:var(--ink)}
tr:last-child td{border-bottom:none}
td:last-child,th:last-child{border-right:none}

code{background:var(--code);padding:1px 6px;border-radius:5px;font-size:.86em;
  font-family:"SFMono-Regular",Consolas,monospace}
.mnem{background:#111827;color:#fde68a;padding:2px 9px;border-radius:6px;
  font-weight:700;letter-spacing:1px;display:inline-block}
.pill{display:inline-block;background:var(--brand-soft);color:var(--brand);
  border-radius:6px;padding:1px 9px;font-size:.8rem;font-weight:600;margin:2px}

figure{margin:14px 0;text-align:center;background:var(--bg);border:1px dashed var(--line);
  border-radius:12px;padding:12px}
figure svg{max-width:100%;height:auto}
figcaption{font-size:.8rem;color:var(--muted);margin-top:8px}

details{border:1px solid var(--line);border-radius:10px;padding:6px 14px;margin:8px 0;background:var(--bg)}
summary{cursor:pointer;font-weight:600}
details[open]{background:var(--card)}

.foot{text-align:center;color:var(--muted);font-size:.8rem;padding:24px 16px}
.foot a{color:var(--brand)}
.backtop{display:inline-block;margin-top:6px;font-size:.82rem;color:var(--brand);text-decoration:none}

/* ---- topic-page breadcrumb + tier badge ---- */
.crumb{display:flex;align-items:center;gap:8px;flex-wrap:wrap;margin:2px 0 14px;font-size:.85rem;color:var(--muted)}
.crumb a{color:var(--brand);text-decoration:none;font-weight:600}
.tierbadge{font-weight:700;border-radius:20px;padding:2px 10px;font-size:.8rem;white-space:nowrap}
.tierbadge.t1{background:#fdecec;color:#c0392b}
.tierbadge.t2{background:#fff2e5;color:#a04000}
.crumb .ord{margin-left:auto;font-variant-numeric:tabular-nums;opacity:.75}
@media (prefers-color-scheme: dark){.tierbadge.t1{background:#3a1e1e;color:#f5a6a6}.tierbadge.t2{background:#3a2a17;color:#f0c08a}}

/* ---- prev / next nav ---- */
.prevnext{display:grid;grid-template-columns:1fr auto 1fr;gap:8px;align-items:stretch;margin:8px 0 2px}
.pn{display:flex;flex-direction:column;justify-content:center;text-decoration:none;color:var(--ink);
  background:var(--card);border:1px solid var(--line);border-radius:12px;padding:10px 13px;font-weight:700;font-size:.9rem;box-shadow:var(--shadow)}
.pn:hover{border-color:var(--brand)}
.pn.next{text-align:right}
.pn small{display:block;font-weight:500;color:var(--muted);font-size:.72rem;margin-top:2px}
.pn-home{display:flex;align-items:center;justify-content:center;text-decoration:none;font-weight:700;
  color:var(--brand);background:var(--brand-soft);border-radius:12px;padding:0 14px;font-size:.85rem;white-space:nowrap}
.pn.empty{visibility:hidden}
@media(max-width:520px){.prevnext{grid-template-columns:1fr 1fr}.pn-home{grid-column:1 / -1;order:3;padding:10px}}

/* ---- home: tier groups ---- */
.group-title{display:flex;align-items:center;gap:9px;margin:26px 4px 2px;font-size:1.05rem;font-weight:800}
.group-title:first-of-type{margin-top:16px}