/* ---- Self-hosted fonts (no CDN; CSP font-src 'self') ---- */
  @font-face{font-family:'Fraunces';font-style:normal;font-weight:500 600;font-display:swap;src:url('/fonts/fraunces-v38-latin-var.woff2') format('woff2');}
  @font-face{font-family:'Inter';font-style:normal;font-weight:400 600;font-display:swap;src:url('/fonts/inter-v20-latin-var.woff2') format('woff2');}
  @font-face{font-family:'JetBrains Mono';font-style:normal;font-weight:500;font-display:swap;src:url('/fonts/jetbrains-mono-v24-latin-500.woff2') format('woff2');}

  /* ============================================================
     TOKENS — LIGHT is the default (unprefixed :root); dark is opt-in.
     Mirrors the app palette so the marketing site and the app match.
     (Copied verbatim from index.css so this page is byte-identical in shell.)
     ============================================================ */
  :root, [data-theme="light"]{
    --bg:#F4F1EA; --surface:#FFFFFF; --card:#FFFFFF; --card-2:#FBF8F1;
    --line:#E7E0D1; --line-2:#DBD2BF;
    --text:#1F2937; --dim:#5B5345; --muted:#857B66;
    --accent:#C2410C; --accent-bri:#D97706; --accent-deep:#9A3412; --on-accent:#FFFFFF;
    --gold:#D9A441; --gold-deep:#B8862B; --ok:#2A7A52;
    --serif:'Fraunces',Georgia,serif;
    --sans:'Inter',-apple-system,BlinkMacSystemFont,system-ui,sans-serif;
    --mono:'JetBrains Mono','SF Mono',Menlo,monospace;
    --shadow:0 20px 50px -28px rgba(31,41,55,0.22);
  }
  [data-theme="dark"]{
    --bg:#14110C; --surface:#1C1813; --card:#251F18; --card-2:#2C2316;
    --line:#3A3225; --line-2:#473826;
    --text:#EDE7D9; --dim:#C9C0AE; --muted:#A89F8C;
    --accent:#F0911F; --accent-bri:#D97706; --accent-deep:#B45309; --on-accent:#2A1B05;
    --gold:#FCD34D; --gold-deep:#E9B838; --ok:#7bbe97;
    --shadow:0 24px 60px -30px rgba(0,0,0,0.7);
  }

  *,*::before,*::after{box-sizing:border-box}
  html{scroll-behavior:smooth}
  body{margin:0;background:var(--bg);color:var(--text);font-family:var(--sans);
    font-size:17px;line-height:1.6;-webkit-font-smoothing:antialiased;
    transition:background .2s ease,color .2s ease}
  a{color:var(--accent);text-decoration:none}
  a:hover{text-decoration:underline;text-underline-offset:3px}
  .mono{font-family:var(--mono)}
  .wrap{max-width:1120px;margin:0 auto;padding:0 24px}

  h1,h2,h3{font-family:var(--serif);font-weight:600;letter-spacing:-0.02em;line-height:1.1;margin:0 0 18px}
  h1{font-size:clamp(38px,5.2vw,56px);line-height:1.05}
  h2.sec{font-size:clamp(28px,3.4vw,38px);margin:10px 0 24px}
  p.lead{color:var(--dim);font-size:clamp(16px,1.3vw,18px);max-width:640px;line-height:1.6}
  .eyebrow,.kick{display:inline-block;font-family:var(--mono);font-size:12px;font-weight:600;
    letter-spacing:0.18em;text-transform:uppercase;color:var(--accent-bri);margin-bottom:14px}

  /* ---- Top bar ---- */
  .topbar{position:sticky;top:0;z-index:30;display:flex;align-items:center;gap:14px;
    padding:14px 24px;max-width:1120px;margin:0 auto;
    background:color-mix(in srgb,var(--bg) 88%,transparent);
    -webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px)}
  .brand{display:flex;align-items:center;gap:10px;color:var(--text)}
  .logo-mark{height:26px;width:auto}
  .wm{font-family:var(--serif);font-weight:600;font-size:20px;letter-spacing:-0.3px}
  .pill{font-family:var(--mono);font-size:10px;font-weight:700;letter-spacing:1px;
    color:var(--on-accent);background:linear-gradient(180deg,var(--gold),var(--gold-deep));
    padding:3px 7px;border-radius:6px}
  .topnav{display:flex;gap:4px;margin-left:14px}
  .navlink{color:var(--dim);font-size:14px;font-weight:500;padding:7px 11px;border-radius:8px}
  .navlink:hover{color:var(--text);background:var(--card);text-decoration:none}
  .navlink.active{color:var(--text);background:var(--card)}
  .topactions{margin-left:auto;display:flex;align-items:center;gap:10px}
  .tbtn{display:inline-flex;align-items:center;justify-content:center;gap:6px;
    font-family:var(--sans);font-size:13.5px;font-weight:600;color:var(--text);
    background:var(--card);border:1px solid var(--line-2);border-radius:9px;
    padding:9px 13px;cursor:pointer}
  .tbtn:hover{border-color:var(--accent)}
  .tbtn.icon{padding:9px;width:40px}
  .btn{display:inline-block;text-align:center;font-weight:700;font-size:14.5px;
    border-radius:10px;padding:11px 18px;border:1px solid transparent;cursor:pointer;
    font-family:var(--sans)}
  .btn.primary{background:linear-gradient(180deg,var(--accent-bri),var(--accent));
    color:var(--on-accent);border-color:var(--accent-deep)}
  .btn.primary:hover{filter:brightness(1.05);text-decoration:none}
  .btn.ghost{background:transparent;color:var(--text);border-color:var(--line-2)}
  .btn.ghost:hover{border-color:var(--accent);text-decoration:none}
  @media(max-width:780px){.topnav{display:none}.tbtn .txt{display:none}}

  /* ---- Sections ---- */
  section.band{border-top:1px solid var(--line);padding:56px 0}
  .callout{background:var(--card);border-left:3px solid var(--gold);padding:24px 28px;border-radius:8px;
    max-width:820px;margin:8px 0 0;font-size:16px;color:var(--text);line-height:1.7}
  .callout strong{color:var(--text)}
  .trust{display:grid;grid-template-columns:repeat(4,1fr);gap:22px;text-align:center;margin-top:40px}
  @media(max-width:760px){.trust{grid-template-columns:repeat(2,1fr)}}
  .stat .num{font-family:var(--serif);font-size:24px;font-weight:600;color:var(--accent);line-height:1.2}
  .stat .label{font-family:var(--mono);font-size:11px;font-weight:600;color:var(--muted);letter-spacing:.08em;margin-top:8px;text-transform:uppercase}

  /* cta band */
  .ctaband{text-align:center;background:var(--card-2);border:1px solid var(--line);border-radius:20px;padding:46px 24px;margin:56px 0}
  .ctaband h2{font-family:var(--serif);font-weight:600;font-size:clamp(26px,3vw,34px);margin:0 0 10px;letter-spacing:-.3px}
  .ctaband p{color:var(--dim);margin:0 auto 22px;max-width:560px}

  footer{border-top:1px solid var(--line);padding:30px 0;color:var(--muted);font-size:13px}
  footer .row{display:flex;gap:16px;flex-wrap:wrap;align-items:center}
  footer a{color:var(--muted);margin-right:14px}
  footer a:hover{color:var(--text)}
  footer .brand{color:var(--text);font-family:var(--serif);font-weight:600;font-size:17px}

/* utilities (were inline style="" attributes) */
.u-ml-auto { margin-left: auto; }
.u-brand-inline { display: inline-flex; align-items: center; gap: 9px; }
.u-h22 { height: 22px; }

/* ============================================================
   PAGE-SPECIFIC — the plug-math explainer
   ============================================================ */
  .math-hero{padding:52px 0 8px;max-width:760px}
  .math-hero h1{margin:8px 0 16px}
  .cta-row{display:flex;gap:12px;flex-wrap:wrap;margin-top:22px}

  /* two-engine split */
  .engines{display:grid;grid-template-columns:1fr 1fr;gap:18px;margin-top:26px;max-width:820px}
  @media(max-width:680px){.engines{grid-template-columns:1fr}}
  .engine{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:24px}
  .engine.a{border-top:3px solid var(--accent)}
  .engine.b{border-top:3px solid var(--gold)}
  .engine .tag{font-family:var(--mono);font-size:11px;letter-spacing:.1em;text-transform:uppercase;color:var(--muted)}
  .engine h3{font-size:19px;margin:6px 0 8px}
  .engine p{color:var(--dim);font-size:14.5px;margin:0;line-height:1.6}

  /* wellbore figure */
  .figure{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:22px;margin-top:26px;box-shadow:var(--shadow)}
  .figure svg{width:100%;height:auto;display:block}
  .figure figcaption{font-family:var(--mono);font-size:12px;color:var(--muted);margin-top:14px;text-align:center;letter-spacing:.02em}

  /* feature list */
  .features{margin-top:10px;max-width:760px}
  .feature{border-left:3px solid var(--line-2);padding:2px 0 2px 20px;margin:24px 0}
  .feature.a{border-color:var(--accent)}
  .feature.b{border-color:var(--accent-deep)}
  .feature.c{border-color:var(--gold)}
  .feature.d{border-color:var(--gold);border-left-style:dashed}
  .feature.e{border-color:var(--muted)}
  .feature .cite{font-family:var(--mono);font-size:12.5px;color:var(--muted);letter-spacing:.02em}
  .feature h3{font-size:19px;margin:3px 0 6px}
  .feature p{color:var(--dim);font-size:15px;margin:0}

  /* plain-english geometry */
  .formula{font-family:var(--mono);background:var(--card-2);border:1px solid var(--line);border-radius:12px;
    padding:18px 20px;margin:22px 0;overflow-x:auto;font-size:15px;color:var(--text);max-width:760px;line-height:1.9}
  .formula .lhs{color:var(--accent)}
  .formula .note{color:var(--muted)}
  .keypoints{max-width:760px;margin:0;padding-left:20px}
  .keypoints li{margin-bottom:.5em;color:var(--dim)}
  .keypoints li strong{color:var(--text)}

  /* worked example table */
  .mtable-wrap{overflow-x:auto;margin:18px 0;max-width:760px}
  table.mtable{border-collapse:collapse;width:100%;font-size:14.5px}
  table.mtable th,table.mtable td{text-align:left;padding:10px 14px;border-bottom:1px solid var(--line)}
  table.mtable th{font-family:var(--mono);font-size:11px;letter-spacing:.06em;text-transform:uppercase;color:var(--muted);font-weight:600}
  table.mtable td.n{font-family:var(--mono);text-align:right;font-variant-numeric:tabular-nums;color:var(--text)}
  table.mtable td.c{font-family:var(--mono);color:var(--dim)}
  table.mtable tr:last-child td{border-bottom:none}
  table.mtable tr.total td{font-weight:700;border-top:2px solid var(--line-2);color:var(--text)}