:root{
  --bg:#f7fafc; --card:#ffffff; --card2:#f7fafc; --text:#1a202c; --dim:#718096;
  --line:rgba(15,23,42,.09); --line2:rgba(15,23,42,.16);
  --green:#16a34a; --green2:#15803d; --cyan:#2563eb; --red:#dc2626; --amber:#c05621;
  --shadow:0 12px 28px rgba(15,23,42,.08); --shadow2:0 6px 16px rgba(15,23,42,.06); --radius:18px;
}   

    * { box-sizing: border-box; }
    html { scroll-behavior: smooth; }
    body {
      margin: 0;
      font-family: "IBM Plex Sans", system-ui, sans-serif;
      background:
        radial-gradient(1200px 500px at 10% -10%, rgba(182, 242, 109, 0.12), transparent 50%),
        radial-gradient(900px 400px at 100% 0%, rgba(127, 211, 106, 0.08), transparent 45%),
        var(--bg);
      color: var(--text);
      line-height: 1.5;
      min-height: 100vh;
    }
/* ---- NAV ---- */
.site-nav{
  position:sticky;top:0;z-index:999;
  background:rgba(255,255,255,.92);backdrop-filter:blur(14px);
  border-bottom:1px solid var(--line);
}
.nav-wrap{
  max-width:92%;margin:0 auto;padding:0 18px;
  display:flex;align-items:center;gap:8px;height:58px;
}
.nav-brand{
  color:var(--green);font-size:17px;font-weight:900;text-decoration:none;
  white-space:nowrap;margin-right:auto;letter-spacing:-.3px;
}
.nav-brand:hover{color:var(--green2)}
.nav-links{display:flex;align-items:center;gap:4px}
.nav-link{
  color:var(--dim);text-decoration:none;font-size:15px;font-weight:700;
  padding:8px 12px;border-radius:8px;white-space:nowrap;
  transition:color .15s ease,background .15s ease;
}
.nav-link:hover,.nav-link.active{color:var(--text);background:rgba(15,23,42,.045)}
.nav-dropdown{position:relative;}
.nav-dropdown-btn{
  display:inline-flex;align-items:center;gap:4px;
  background:none;border:none;cursor:pointer;
  color:var(--dim);font-size:15px;font-weight:700;
  padding:8px 12px;border-radius:8px;white-space:nowrap;
  transition:color .15s ease,background .15s ease;
}
.nav-dropdown-btn:hover,.nav-dropdown-btn.open{color:var(--text);background:rgba(15,23,42,.045)}
/* Mega menu: right-anchored so it never overflows the right edge of the viewport,
   width capped to viewport so it never overflows the left edge either,
   scrolls internally if the content is taller than the viewport. */
.nav-dropdown-menu{
  display:none;position:absolute;top:calc(100% + 8px);right:0;left:auto;
  background:var(--card);border:1px solid var(--line2);border-radius:14px;
  padding:14px;width:min(880px,calc(100vw - 32px));
  max-height:calc(100vh - 90px);overflow-y:auto;-webkit-overflow-scrolling:touch;
  box-shadow:var(--shadow);z-index:1000;
}
.nav-dropdown-menu.open{
  display:grid;grid-template-columns:repeat(3,1fr);gap:2px 14px;
  animation:megamenuIn .16s ease;
}
.nav-dropdown-menu a{
  display:flex;align-items:flex-start;gap:8px;
  padding:9px 10px;border-radius:9px;
  color:var(--dim);text-decoration:none;font-size:14px;font-weight:600;line-height:1.35;
  transition:color .13s ease,background .13s ease;
}
.nav-dropdown-menu a:hover{color:var(--text);background:rgba(15,23,42,.05)}
@keyframes megamenuIn{from{opacity:0;transform:translateY(-4px)}to{opacity:1;transform:translateY(0)}}
/* ---- BREADCRUMB ---- */
.breadcrumb{font-size:14px;color:var(--dim);padding:12px 0 0;display:flex;gap:6px;align-items:center;flex-wrap:wrap}
.breadcrumb a{color:var(--cyan);text-decoration:none}
.breadcrumb a:hover{text-decoration:underline}
.breadcrumb span{color:var(--dim)}
/* Tablet: mega menu narrows to 2 columns and a smaller panel so it fits mid-size viewports */
@media(max-width:1024px) and (min-width:769px){
  .nav-dropdown-menu{width:min(600px,calc(100vw - 32px))}
  .nav-dropdown-menu.open{grid-template-columns:repeat(2,1fr)}
}
.nav-toggle{
  display:none;background:none;border:1px solid var(--line2);color:var(--dim);
  padding:6px 10px;border-radius:8px;cursor:pointer;font-size:18px;
}
/* ---- LAYOUT ---- */
.wrap{max-width:92%;margin:0 auto;padding:18px 16px 0}
.page-wrap{max-width:82%;margin:0 auto;padding:24px 16px 0}

    .wrap {
      width: min(1120px, calc(100% - 32px));
      margin: 0 auto;
      padding: 28px 0 64px;
    }

    header {
      display: grid;
      gap: 14px;
      margin-bottom: 22px;
    }

    .kicker {
      display: inline-flex;
      align-items: center;
      gap: 8px;
      font-size: 12px;
      letter-spacing: 0.14em;
      text-transform: uppercase;
      color: var(--mint);
      font-weight: 600;
    }

    h1 {
      font-family: "IBM Plex Serif", Georgia, serif;
      font-size: clamp(2rem, 4vw, 3.15rem);
      font-weight: 600;
      letter-spacing: -0.03em;
      line-height: 1.12;
      margin: 0;
    }

    .lede {
      max-width: 62ch;
      color: var(--muted);
      margin: 0;
      font-size: 1.05rem;
    }

    .disclaimer {
      display: flex;
      gap: 12px;
      align-items: flex-start;
      padding: 14px 16px;
      border: 1px solid rgba(239, 179, 90, 0.35);
      background: rgba(239, 179, 90, 0.08);
      border-radius: 14px;
      color: #333;
      font-size: 0.95rem;
    }

    .disclaimer strong { color: #333; }
/* ---- FOOTER ---- */
.site-footer{
  text-align:center;color:var(--dim);font-size:13.5px;margin-top:40px;
  padding:20px 16px;border-top:1px solid var(--line);line-height:1.8;
}
.site-footer a{color:var(--cyan);text-decoration:none}
.site-footer a:hover{text-decoration:underline}
.footer-nav{display:flex;gap:14px;justify-content:center;flex-wrap:wrap;margin-bottom:10px}

    .layout {
      display: grid;
      grid-template-columns: minmax(0, 1.08fr) minmax(320px, 0.92fr);
      gap: 22px;
      align-items: start;
    }

    .panel {
      background: linear-gradient(180deg, var(--panel), var(--bg-2));
      border: 1px solid var(--line);
      border-radius: var(--radius);
      box-shadow: var(--shadow);
    }

    form { padding: 22px; display: grid; gap: 18px; }

    .section-title {
      margin: 0 0 2px;
      font-size: 0.78rem;
      letter-spacing: 0.12em;
      text-transform: uppercase;
      color: var(--mint);
      font-weight: 600;
    }

    .grid-2 {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 14px;
    }
    .btn-calc{
  width:100%;margin-top:14px;padding:14px 14px;border:none;border-radius:12px;cursor:pointer;
  color:#04150d;font-size:17px;font-weight:900;
  background:linear-gradient(90deg,var(--green),var(--cyan));
  box-shadow:0 10px 24px rgba(22,163,74,.14);transition:transform .14s ease,box-shadow .14s ease
}
.btn-calc:hover{transform:translateY(-1px);box-shadow:0 14px 28px rgba(22,163,74,.22)}

    label {
      display: grid;
      gap: 6px;
      font-size: 0.92rem;
      font-weight: 500;
    }

    .hint {
      font-size: 0.8rem;
      color: var(--muted);
      font-weight: 400;
    }

    input, select {
      width: 100%;
      border: 1px solid var(--line);
      background: var(--panel-2);
      color: var(--text);
      border-radius: 12px;
      padding: 11px 12px;
      font: inherit;
      outline: none;
    }

    input:focus, select:focus {
      border-color: var(--mint);
      box-shadow: 0 0 0 3px rgba(182, 242, 109, 0.18);
    }

    .actions {
      display: flex;
      gap: 10px;
      flex-wrap: wrap;
      padding-top: 4px;
    }

    button {
      font: inherit;
      border: 0;
      border-radius: 999px;
      padding: 11px 18px;
      cursor: pointer;
      font-weight: 600;
    }

    .primary {
      background: var(--mint);
      color: #14210f;
    }

    .ghost {
      background: transparent;
      color: var(--text);
      border: 1px solid var(--line);
    }

    .results {
      position: sticky;
      top: 16px;
      padding: 22px;
      display: grid;
      gap: 16px;
    }

    .soh-block {
      display: grid;
      grid-template-columns: 118px 1fr;
      gap: 16px;
      align-items: center;
    }

    .gauge {
      width: 118px;
      height: 118px;
    }

    .soh-copy h2 {
      margin: 0;
      font-size: 0.8rem;
      letter-spacing: 0.1em;
      text-transform: uppercase;
      color: var(--muted);
      font-weight: 600;
    }

    .soh-value {
      font-family: "IBM Plex Serif", Georgia, serif;
      font-size: 2.6rem;
      line-height: 1;
      margin: 4px 0 6px;
    }

    .band { color: var(--muted); font-size: 0.9rem; }

    .metrics {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 10px;
    }

    .metric {
      background: rgba(255,255,255,0.03);
      border: 1px solid var(--line);
      border-radius: 14px;
      padding: 12px;
    }

    .metric span {
      display: block;
      color: var(--muted);
      font-size: 0.78rem;
      letter-spacing: 0.06em;
      text-transform: uppercase;
    }

    .metric strong {
      display: block;
      margin-top: 4px;
      font-size: 1.25rem;
    }

    .uncertainty, .method {
      font-size: 0.92rem;
      color: #1a202c;
    }

    .uncertainty h3, .method h3 {
      margin: 0 0 6px;
      font-size: 0.95rem;
    }

    .error {
      color: var(--coral);
      font-size: 0.9rem;
      min-height: 1.2em;
    }

    footer {
      margin-top: 28px;
      color: var(--muted);
      font-size: 0.88rem;
    }

    @media (max-width: 860px) {
      .layout, .soh-block, .grid-2, .metrics {
        grid-template-columns: 1fr;
      }
      .results { position: static; }
    }
  /* ---- RESPONSIVE ---- */
@media(max-width:768px){
  .nav-links{
    display:none;position:absolute;top:58px;left:0;right:0;
    flex-direction:column;align-items:stretch;gap:0;
    max-height:calc(100vh - 58px);overflow-y:auto;-webkit-overflow-scrolling:touch;
    background:rgba(255,255,255,.98);border-bottom:1px solid var(--line);padding:10px;
  }
  .nav-links.open{display:flex}
  .nav-toggle{display:block}
  .nav-dropdown{position:static;width:100%}
  .nav-dropdown-menu{
    position:static;transform:none;box-shadow:none;
    background:rgba(15,23,42,.035);border:none;border-radius:10px;
    margin-top:4px;min-width:0;max-width:100%;padding:6px;width:100%;
  }
  .nav-dropdown-menu.open{display:grid;grid-template-columns:1fr;gap:2px;width:100%}
  .nav-dropdown-btn,.nav-link{width:100%;text-align:left;padding:11px 14px;justify-content:space-between}
  .grid,.grid-2{grid-template-columns:1fr}
  .calc-card{padding:18px}
  .hero h1{font-size:27px}
  .card{padding:16px}
  .page-wrap{padding:16px 12px 0}
  .form-grid{grid-template-columns:1fr}
  .results-grid{grid-template-columns:repeat(2,1fr)}
  .mode-tab{font-size:13.5px;padding:9px 4px}
  .action-bar{gap:6px}
  .action-btn{font-size:13px;padding:7px 11px}
  .preset-buttons{gap:6px}
  .preset-btn{font-size:13px;padding:7px 11px}
  .chart-container{height:260px;padding:10px}
  .share-section{flex-direction:column}
  .share-btn{min-width:0}
}