:root{
  --bg:#0f1117; --panel:#171b24; --panel2:#1d222d; --border:#2a3140;
  --text:#e8eaed; --muted:#8b93a3; --green:#26d07c; --red:#f6465d;
  --accent:#f0b90b; --inputbg:#10131a; --sidebar:#12151d;
  --topbar-h:56px; --sidebar-w:250px;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  background:var(--bg); color:var(--text);
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  font-size:15px; line-height:1.5;
}
a{color:inherit;text-decoration:none}

/* ---------- Top bar ---------- */
.topbar{
  position:sticky; top:0; z-index:30; height:var(--topbar-h);
  display:flex; align-items:center; gap:14px; padding:0 18px;
  background:#0b0d13; border-bottom:1px solid var(--border);
}
.brand{font-weight:700; font-size:17px; letter-spacing:.2px}
.brand-mark{color:var(--accent)}
.menu-btn{display:none; font-size:22px; cursor:pointer; color:var(--muted); user-select:none}

/* ---------- Layout ---------- */
.layout{display:flex; min-height:calc(100vh - var(--topbar-h))}
.sidebar{
  width:var(--sidebar-w); flex-shrink:0; background:var(--sidebar);
  border-right:1px solid var(--border); padding:16px 12px;
  position:sticky; top:var(--topbar-h); height:calc(100vh - var(--topbar-h)); overflow-y:auto;
}
.content{flex:1; padding:28px 32px; max-width:900px}

/* ---------- Nav ---------- */
.nav-home,.nav-link{
  display:block; padding:9px 12px; border-radius:8px; color:var(--muted);
  font-size:14px; transition:.12s;
}
.nav-home:hover,.nav-link:hover{background:var(--panel2); color:var(--text)}
.nav-home.active,.nav-link.active{background:var(--panel2); color:var(--accent); font-weight:600}
.nav-section{
  margin:22px 12px 4px; padding-bottom:6px;
  font-size:12px; font-weight:700; letter-spacing:.03em; color:var(--text);
  border-bottom:1px solid var(--border);
}
.nav-group{margin-top:14px}
.nav-cat{
  font-size:11px; text-transform:uppercase; letter-spacing:.08em;
  color:#5b6472; padding:0 12px 6px;
}

/* ---------- Landing / hero ---------- */
.hero{
  text-align:center; padding:34px 20px 30px; margin-bottom:26px;
  background:radial-gradient(120% 140% at 50% 0%, rgba(38,208,124,.10), transparent 60%);
  border:1px solid var(--border); border-radius:16px;
}
.hero-brand{font-size:34px; margin:0 0 10px; letter-spacing:.3px}
.hero-slogan{font-size:19px; font-weight:600; margin:0 auto 12px; max-width:560px; color:var(--green)}
.hero-sub{color:var(--muted); margin:0 auto; max-width:600px; font-size:14px; line-height:1.6}
.hero-cta{display:inline-block; margin-top:20px; padding:11px 20px; border-radius:9px; background:var(--accent); color:#1a1a1a; font-weight:700; font-size:14px}
.hero-cta:hover{filter:brightness(1.05)}

.features{display:grid; grid-template-columns:repeat(auto-fit,minmax(190px,1fr)); gap:16px; margin-bottom:26px}
.feature{background:var(--panel); border:1px solid var(--border); border-radius:12px; padding:18px}
.feature-ic{font-size:22px; margin-bottom:8px}
.feature h3{margin:0 0 6px; font-size:15px}
.feature p{margin:0; color:var(--muted); font-size:13px; line-height:1.55}

.seo-intro{background:var(--panel); border:1px solid var(--border); border-radius:12px; padding:18px 20px; margin-bottom:30px}
.seo-intro p{margin:0; color:var(--muted); font-size:14px; line-height:1.7}
.seo-intro strong{color:var(--text); font-weight:600}

.subsection-title{font-size:13px; text-transform:uppercase; letter-spacing:.06em; color:var(--muted); margin:22px 0 12px}

.faq{margin-top:36px}
.faq-item{border-bottom:1px solid var(--border); padding:14px 0}
.faq-item h3{margin:0 0 6px; font-size:15px}
.faq-item p{margin:0; color:var(--muted); font-size:14px; line-height:1.6}

.section-title{font-size:16px; margin:30px 0 12px; padding-bottom:6px; border-bottom:1px solid var(--border)}
.card-grid{display:grid; grid-template-columns:repeat(auto-fill,minmax(240px,1fr)); gap:16px}
.calc-card{
  display:block; background:var(--panel); border:1px solid var(--border);
  border-radius:12px; padding:18px; transition:.15s;
}
.calc-card:hover{border-color:var(--accent); transform:translateY(-2px)}
.calc-card-cat{font-size:11px; text-transform:uppercase; letter-spacing:.06em; color:var(--accent)}
.calc-card h3{margin:8px 0 6px; font-size:16px}
.calc-card p{margin:0; color:var(--muted); font-size:13px}

/* ---------- Calculator UI (shared by all calc pages) ---------- */
.calc-head{margin-bottom:18px}
.calc-head h1{font-size:22px; margin:0 0 4px}
.calc-head p{color:var(--muted); margin:0; font-size:14px}
.panel{background:var(--panel); border:1px solid var(--border); border-radius:12px; padding:22px; max-width:560px}
.side-toggle{display:flex; border:1px solid var(--border); border-radius:9px; overflow:hidden; margin-bottom:6px}
.side-toggle button{
  flex:1; padding:12px; background:var(--panel2); color:var(--muted);
  border:none; font-size:15px; font-weight:600; cursor:pointer; transition:.15s;
}
.side-toggle button.long.active{background:var(--green); color:#06231a}
.side-toggle button.short.active{background:var(--red); color:#2a060c}
.form-label{display:block; font-size:12px; color:var(--muted); margin:16px 0 6px}
.field{display:flex; align-items:center; background:var(--inputbg); border:1px solid var(--border); border-radius:9px; padding:0 14px}
.field input{flex:1; width:100%; background:transparent; border:none; color:var(--text); font-size:16px; padding:12px 0; outline:none}
.field .unit{color:var(--muted); font-size:13px; font-weight:600; margin-left:8px}
.field select{background:var(--panel2); color:var(--text); border:1px solid var(--border); border-radius:6px; padding:6px 8px; font-size:13px; outline:none; cursor:pointer}
.row{display:flex; gap:14px}
.row>div{flex:1}
.btn-calc{width:100%; margin-top:20px; padding:14px; background:var(--accent); color:#1a1a1a; border:none; border-radius:9px; font-size:16px; font-weight:700; cursor:pointer}
.btn-calc:hover{filter:brightness(1.05)}
.err{color:var(--red); font-size:13px; margin-top:12px; min-height:1px}
.results{margin-top:22px; border-top:1px solid var(--border); padding-top:18px}
.results h2{font-size:15px; margin:0 0 12px}
.res-row{display:flex; justify-content:space-between; align-items:baseline; padding:9px 0; border-bottom:1px solid rgba(255,255,255,.05); font-size:14px}
.res-row .k{color:var(--muted)}
.res-row .v{font-weight:600; font-variant-numeric:tabular-nums}
.res-row.big .v{font-size:18px}
.pos{color:var(--green)!important} .neg{color:var(--red)!important}
.note{color:var(--muted); font-size:11px; margin-top:16px; line-height:1.6; max-width:560px}
.note code{background:var(--panel2); padding:1px 5px; border-radius:4px}

/* ---------- Footer ---------- */
.sitefoot{padding:20px 32px; color:#5b6472; font-size:12px; border-top:1px solid var(--border)}

/* ---------- Mobile: collapsible sidebar via checkbox ---------- */
.nav-scrim{display:none}
@media (max-width:760px){
  .menu-btn{display:inline-block}
  .content{padding:20px 18px}
  .sidebar{
    position:fixed; top:var(--topbar-h); left:0; z-index:25;
    transform:translateX(-100%); transition:transform .2s;
  }
  .nav-scrim{
    display:block; position:fixed; inset:var(--topbar-h) 0 0 0; z-index:20;
    background:rgba(0,0,0,.5); opacity:0; pointer-events:none; transition:opacity .2s;
  }
  .nav-toggle:checked ~ .layout .sidebar{transform:translateX(0)}
  .nav-toggle:checked ~ .layout .nav-scrim{opacity:1; pointer-events:auto}
}