:root {
  --bg:#f5f7fa; --card:#fff; --text:#17202a; --muted:#64748b; --border:#d9e0e7;
  --accent:#2563eb; --accent-dark:#1d4ed8; --danger:#b91c1c; --success:#166534;
  --warning:#92400e; --warning-bg:#fffbeb; --warning-border:#fde68a;
  --info-bg:#eff6ff; --info-border:#bfdbfe; --info-text:#1e3a8a;
  --shadow:0 2px 12px rgba(15,23,42,.06);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--text);font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;line-height:1.5}
a{color:#1d4ed8}
a:hover{text-decoration-thickness:2px}
.container, main{max-width:1080px;margin:0 auto}
header{background:#111827;color:#fff;padding:22px 18px 28px}
.site-nav{display:flex;justify-content:space-between;align-items:center;gap:18px;margin-bottom:24px}
.site-brand{color:#fff;text-decoration:none;font-weight:800;font-size:1.08rem;white-space:nowrap}
.site-links{display:flex;gap:16px;flex-wrap:wrap}
.site-links a{color:#dbeafe;text-decoration:none;font-weight:650;font-size:.94rem}
.site-links a:hover,.site-links a:focus{color:#fff;text-decoration:underline}
header h1{margin:0 0 7px;font-size:clamp(1.55rem,4vw,2.25rem);line-height:1.15}
header p{margin:0;color:#cbd5e1;max-width:780px}
main{padding:24px 16px 52px}
.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px}
.card{background:var(--card);border:1px solid var(--border);border-radius:12px;box-shadow:var(--shadow);padding:20px}
.card h2:first-child,.card h3:first-child{margin-top:0}
.full{grid-column:1/-1}
h2{margin:0 0 14px;font-size:1.25rem} h3{margin:20px 0 10px;font-size:1.03rem}
p{margin:0 0 14px}.lead{font-size:1.05rem;color:#334155}
.fields{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}
.field.full-field{grid-column:1/-1}
label{display:block;font-size:.9rem;font-weight:700;margin-bottom:6px}
input,select,button{width:100%;border:1px solid #cbd5e1;border-radius:8px;min-height:42px;padding:9px 11px;font:inherit;background:#fff;color:var(--text)}
input:focus,select:focus,button:focus-visible,a:focus-visible{outline:3px solid rgba(37,99,235,.22);outline-offset:2px}
button{cursor:pointer;background:var(--accent);color:#fff;border-color:var(--accent);font-weight:750}
button:hover{background:var(--accent-dark)}
button.secondary{background:#fff;color:var(--text);border-color:var(--border)}
.actions{display:flex;gap:10px;flex-wrap:wrap;margin-top:16px}.actions button{width:auto;min-width:170px}
.hint{margin-top:5px;color:var(--muted);font-size:.82rem}
.notice,.warning,.error,.success{padding:12px 14px;border-radius:8px;margin:0 0 16px;font-size:.92rem}
.notice{background:var(--info-bg);border:1px solid var(--info-border);color:var(--info-text)}
.warning{background:var(--warning-bg);border:1px solid var(--warning-border);color:var(--warning)}
.error{display:none;background:#fef2f2;border:1px solid #fecaca;color:var(--danger)}
.success{background:#f0fdf4;border:1px solid #bbf7d0;color:var(--success)}
.results{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:12px}
.metric{border:1px solid var(--border);border-radius:10px;padding:14px;background:#fff}
.metric .label{color:var(--muted);font-size:.82rem;margin-bottom:5px}.metric .value{font-size:1.18rem;font-weight:800;overflow-wrap:anywhere}
.equation{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;background:#f8fafc;border:1px solid #e2e8f0;border-radius:8px;padding:12px;overflow-x:auto;margin:10px 0 14px}
.tool-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px}
.tool-card{display:block;background:#fff;border:1px solid var(--border);border-radius:11px;padding:17px;text-decoration:none;color:inherit;box-shadow:var(--shadow)}
.tool-card:hover{border-color:#93c5fd}.tool-card strong{display:block;font-size:1.03rem;margin-bottom:5px;color:#0f172a}.tool-card span{color:var(--muted);font-size:.92rem}
.pill{display:inline-block;border:1px solid #cbd5e1;border-radius:999px;padding:2px 8px;font-size:.75rem;color:#475569;background:#fff;margin-left:6px}
.small{font-size:.86rem;color:var(--muted)}
ul.compact{margin:8px 0 14px;padding-left:20px}ul.compact li{margin:5px 0}
.table-wrap{overflow-x:auto}table{width:100%;border-collapse:collapse;font-size:.92rem}th,td{text-align:left;border-bottom:1px solid #e5e7eb;padding:9px 8px}th{color:#475569;background:#f8fafc}
footer{background:#111827;color:#cbd5e1;padding:22px 16px;font-size:.9rem}
footer .container{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap}.footer-links{display:flex;gap:14px;flex-wrap:wrap}footer a{color:#e2e8f0;text-decoration:none}footer a:hover,footer a:focus{text-decoration:underline;color:#fff}
@media(max-width:760px){.grid,.fields,.tool-grid,.results{grid-template-columns:1fr}.site-nav{align-items:flex-start;flex-direction:column}.site-links{gap:12px}.actions button{width:100%}.field.full-field{grid-column:auto}}

/* Multi-layer heat-transfer calculator */
.layer-heading-row{display:flex;justify-content:space-between;gap:16px;align-items:flex-end;flex-wrap:wrap;margin-bottom:14px}
.layer-add-actions{display:flex;gap:8px;flex-wrap:wrap}.layer-add-actions button{width:auto;min-width:0}
.thermal-layers{display:grid;gap:12px}
.thermal-layer{border:1px solid var(--border);border-radius:10px;background:#f8fafc;padding:14px}
.thermal-layer-head{display:flex;justify-content:space-between;gap:12px;align-items:center;margin-bottom:12px}
.layer-number{display:inline-grid;place-items:center;width:28px;height:28px;border-radius:999px;background:#e2e8f0;color:#334155;font-weight:800;margin-right:8px}
.layer-controls{display:flex;gap:6px}.icon-button{width:38px;min-width:38px;min-height:38px;padding:4px}.icon-button:disabled{opacity:.4;cursor:not-allowed}
.input-unit{display:grid;grid-template-columns:minmax(0,1fr) minmax(118px,.7fr);gap:7px}
.layer-resistance{margin-top:10px;padding-top:9px;border-top:1px dashed #cbd5e1}
.thermal-results{grid-template-columns:repeat(3,minmax(0,1fr))}
@media(max-width:760px){.layer-heading-row{align-items:stretch}.layer-add-actions{display:grid;grid-template-columns:1fr}.layer-add-actions button{width:100%}.input-unit{grid-template-columns:1fr}.thermal-results{grid-template-columns:1fr}}