/* GPT-inspired marketing: generous space, soft gradients, mono + one accent */
:root{
  --bg:#fff;
  --bg-soft:#f7f7f8;
  --ink:#0d0d0d;
  --ink-2:#5d5d5d;
  --ink-3:#8f8f8f;
  --line:#e8e8e8;
  --line-soft:#f0f0f0;
  --accent:#10a37f; /* OpenAI sage */
  --accent-2:#5b5bd6;
  --radius:18px;
  --font: "Inter", "SF Pro Display", "SF Pro Text", -apple-system, BlinkMacSystemFont,
    "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:var(--bg);
  color:var(--ink);
  font-family:var(--font);
  font-size:16px;
  line-height:1.7;
  -webkit-font-smoothing:antialiased;
  -moz-osx-font-smoothing:grayscale;
}
a{color:inherit;text-decoration:none}
.wrap{width:min(1120px, 100% - 48px);margin:0 auto}
.tiny{font-size:13px}
h1,h2,h3{margin:0;font-weight:650;letter-spacing:-.035em;line-height:1.15}

/* ---------- nav ---------- */
.nav{
  position:sticky;top:0;z-index:60;
  background:rgba(255,255,255,.82);
  backdrop-filter:saturate(1.6) blur(16px);
  -webkit-backdrop-filter:saturate(1.6) blur(16px);
  border-bottom:1px solid transparent;
}
.nav-in{
  display:flex;align-items:center;gap:28px;
  min-height:64px;
}
.brand{
  display:inline-flex;align-items:center;gap:10px;
  font-weight:650;font-size:16px;letter-spacing:-.02em;
}
.mark{
  width:22px;height:22px;border-radius:8px;
  background:
    radial-gradient(circle at 30% 30%, #fff 0 18%, transparent 19%),
    linear-gradient(135deg, #10a37f, #5b5bd6);
  box-shadow:inset 0 0 0 1px rgba(255,255,255,.25);
}
.mark.sm{width:16px;height:16px;border-radius:6px}
.nav-links{display:flex;gap:4px;flex:1}
.nav-links a{
  padding:8px 12px;font-size:14px;color:var(--ink-2);font-weight:500;border-radius:999px;
}
.nav-links a:hover{background:var(--bg-soft);color:var(--ink)}
.nav-cta{display:flex;align-items:center;gap:10px}
.btn-ghost{
  padding:8px 14px;font-size:14px;font-weight:550;color:var(--ink-2);border-radius:999px;
}
.btn-ghost:hover{background:var(--bg-soft);color:var(--ink)}
.btn-dark{
  display:inline-flex;align-items:center;justify-content:center;
  padding:9px 16px;font-size:14px;font-weight:600;
  background:var(--ink);color:#fff;border-radius:999px;
}
.btn-dark:hover{background:#2a2a2a}
.nav-burger{
  display:none;width:40px;height:40px;border:0;background:transparent;
  padding:10px;cursor:pointer;
}
.nav-burger span{display:block;height:1.5px;background:var(--ink);margin:6px 0;border-radius:2px}
.nav-drawer{
  display:none;flex-direction:column;gap:4px;padding:8px 24px 20px;
  border-top:1px solid var(--line-soft);background:rgba(255,255,255,.96);
}
.nav-drawer a{padding:12px 4px;font-size:15px;font-weight:550;color:var(--ink-2)}
.nav-drawer .btn-dark{margin-top:8px;color:#fff}
.nav-drawer.open{display:flex}

/* ---------- hero ---------- */
.hero{
  position:relative;overflow:hidden;
  padding:72px 0 0;
}
.hero-glow{
  position:absolute;border-radius:50%;filter:blur(80px);opacity:.55;pointer-events:none;
}
.hero-glow.g1{
  width:520px;height:520px;left:-120px;top:-80px;
  background:radial-gradient(circle, rgba(16,163,127,.35), transparent 70%);
}
.hero-glow.g2{
  width:560px;height:560px;right:-140px;top:20px;
  background:radial-gradient(circle, rgba(91,91,214,.28), transparent 70%);
}
.hero-in{position:relative;text-align:center;max-width:820px}
.pill{
  display:inline-flex;align-items:center;gap:8px;
  padding:6px 14px;border-radius:999px;
  background:rgba(16,163,127,.1);color:#0d8f6f;
  font-size:13px;font-weight:600;letter-spacing:.01em;
}
.hero h1{
  margin:22px 0 18px;
  font-size:clamp(40px, 7.2vw, 68px);
  font-weight:700;letter-spacing:-.045em;line-height:1.05;
}
.grad{
  background:linear-gradient(120deg, #10a37f 0%, #5b5bd6 55%, #7c7cf0 100%);
  -webkit-background-clip:text;background-clip:text;color:transparent;
}
.lead{
  margin:0 auto;max-width:34em;
  font-size:clamp(17px, 2.2vw, 20px);
  color:var(--ink-2);line-height:1.75;font-weight:400;
}
.hero-actions{
  display:flex;justify-content:center;gap:12px;flex-wrap:wrap;margin:32px 0 22px;
}
.btn-primary{
  display:inline-flex;align-items:center;justify-content:center;
  padding:14px 26px;font-size:16px;font-weight:600;
  background:var(--ink);color:#fff;border-radius:999px;
  box-shadow:0 8px 28px rgba(0,0,0,.12);
}
.btn-primary:hover{transform:translateY(-1px);background:#222}
.btn-line{
  display:inline-flex;align-items:center;justify-content:center;
  padding:14px 22px;font-size:16px;font-weight:550;
  color:var(--ink);border:1px solid var(--line);border-radius:999px;background:#fff;
}
.btn-line:hover{background:var(--bg-soft)}
.hero-meta{
  display:flex;justify-content:center;align-items:center;gap:14px;flex-wrap:wrap;
  color:var(--ink-3);font-size:13.5px;font-weight:500;
}
.dot-sep{width:3px;height:3px;border-radius:50%;background:var(--ink-3);opacity:.6}

/* ---------- product mock ---------- */
.mock-wrap{margin-top:56px;position:relative;padding-bottom:24px}
.mock{
  border-radius:20px;overflow:hidden;
  background:#fff;
  border:1px solid rgba(0,0,0,.06);
  box-shadow:
    0 1px 0 rgba(255,255,255,.8) inset,
    0 30px 80px -20px rgba(20,20,40,.22),
    0 8px 24px -8px rgba(20,20,40,.1);
}
.mock-bar{
  display:flex;align-items:center;gap:8px;
  padding:12px 16px;background:#fafafa;border-bottom:1px solid var(--line-soft);
}
.mock-bar > span{
  width:10px;height:10px;border-radius:50%;background:#e5e5e5;
}
.mock-bar > span:nth-child(1){background:#ff5f57}
.mock-bar > span:nth-child(2){background:#febc2e}
.mock-bar > span:nth-child(3){background:#28c840}
.mock-url{
  margin-left:12px;flex:1;text-align:center;
  font-size:12px;color:var(--ink-3);font-weight:500;
}
.mock-body{display:grid;grid-template-columns:180px 1fr;min-height:340px}
.mock-side{
  padding:18px 14px;background:#fbfbfb;border-right:1px solid var(--line-soft);
}
.mock-brand{
  display:flex;align-items:center;gap:8px;font-size:13px;font-weight:650;margin-bottom:18px;
}
.mock-nav{
  padding:9px 12px;border-radius:10px;font-size:13px;color:var(--ink-2);font-weight:550;margin-bottom:4px;
}
.mock-nav.on{background:#fff;color:var(--ink);box-shadow:0 1px 3px rgba(0,0,0,.06)}
.mock-main{padding:22px 24px}
.mock-head{display:flex;justify-content:space-between;align-items:center;gap:16px}
.mock-kid{font-size:20px;font-weight:650;letter-spacing:-.03em}
.mock-kid em{
  font-style:normal;font-size:11px;font-weight:650;
  background:#111;color:#fff;padding:3px 8px;border-radius:999px;margin-left:8px;
  vertical-align:middle;
}
.mock-sub{font-size:12px;color:var(--ink-3);margin-top:4px}
.mock-ring{
  width:58px;height:58px;border-radius:50%;
  background:conic-gradient(#10a37f 0 24%, #eee 0);
  display:grid;place-items:center;
}
.mock-ring b{
  width:44px;height:44px;border-radius:50%;background:#fff;
  display:grid;place-items:center;font-size:12px;font-weight:700;
}
.mock-subjects{margin:22px 0 18px;display:grid;gap:10px}
.ms{display:grid;grid-template-columns:48px 1fr;gap:10px;align-items:center}
.ms-name{font-size:12px;font-weight:650}
.ms-name.yw{color:#e11d48}.ms-name.sx{color:#2563eb}
.ms-name.yy{color:#7c3aed}.ms-name.kx{color:#059669}
.ms-bar{height:8px;border-radius:99px;background:#f0f0f0;overflow:hidden}
.ms-bar i{
  display:block;height:100%;border-radius:99px;
  background:linear-gradient(90deg, #10a37f, #5b5bd6);
}
.mock-cards{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}
.mc{
  padding:12px 12px;border-radius:12px;border:1px solid var(--line-soft);background:#fff;
}
.mc.hot{border-color:rgba(16,163,127,.35);background:rgba(16,163,127,.06)}
.mc b{display:block;font-size:12.5px;font-weight:650;letter-spacing:-.01em}
.mc span{font-size:11px;color:var(--ink-3)}

/* ---------- sections ---------- */
.section{padding:110px 0}
.section.alt{background:var(--bg-soft)}
.sec-label{
  display:inline-flex;padding:5px 12px;border-radius:999px;
  background:rgba(16,163,127,.1);color:#0d8f6f;
  font-size:12px;font-weight:650;letter-spacing:.06em;text-transform:uppercase;
  margin-bottom:18px;
}
.sec-h{
  font-size:clamp(30px, 4.5vw, 44px);
  max-width:14em;
}
.sec-p{
  margin:16px 0 0;max-width:36em;
  font-size:18px;color:var(--ink-2);
}

.duo{
  display:grid;grid-template-columns:1fr 1fr;gap:18px;margin-top:42px;
}
.duo-card{
  background:#fff;border:1px solid var(--line-soft);border-radius:22px;
  padding:32px 28px;
}
.duo-card.dark{
  background:#111;color:#fff;border-color:#222;
}
.duo-card.dark p,.duo-card.dark li{color:rgba(255,255,255,.72)}
.duo-tag{
  display:inline-flex;padding:4px 10px;border-radius:999px;
  background:rgba(16,163,127,.12);color:#0d8f6f;
  font-size:12px;font-weight:700;letter-spacing:.04em;
}
.duo-card.dark .duo-tag{background:rgba(255,255,255,.12);color:#fff}
.duo-card h3{font-size:24px;margin:14px 0 10px}
.duo-card p{margin:0 0 16px;color:var(--ink-2);font-size:15.5px}
.duo-card ul{margin:0;padding-left:1.15em}
.duo-card li{margin:8px 0;font-size:14.5px;color:var(--ink-2)}

.grid-3{
  display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin-top:42px;
}
.f-card{
  background:#fff;border:1px solid var(--line-soft);border-radius:20px;
  padding:26px 22px;transition:transform .2s ease, box-shadow .2s ease;
}
.f-card:hover{
  transform:translateY(-3px);
  box-shadow:0 18px 40px -18px rgba(20,20,40,.18);
}
.f-ic{
  width:42px;height:42px;border-radius:14px;
  display:grid;place-items:center;
  background:linear-gradient(145deg, rgba(16,163,127,.12), rgba(91,91,214,.12));
  color:#111;font-weight:800;font-size:16px;margin-bottom:16px;
}
.f-card h3{font-size:18px;margin-bottom:8px}
.f-card p{margin:0;color:var(--ink-2);font-size:14.5px}

/* library numbers */
.lib{
  display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin:42px 0 28px;
}
.lib-num{
  padding:28px 22px;border-radius:20px;background:var(--bg-soft);
  border:1px solid var(--line-soft);
}
.big{
  font-size:clamp(40px, 6vw, 56px);font-weight:700;letter-spacing:-.05em;
  background:linear-gradient(120deg, #10a37f, #5b5bd6);
  -webkit-background-clip:text;background-clip:text;color:transparent;
  line-height:1;
}
.lib-num p{margin:10px 0 0;color:var(--ink-2);font-size:14.5px}

.stack-cards{display:grid;gap:12px}
.sc{
  display:grid;grid-template-columns: 200px 1fr;gap:20px;align-items:start;
  padding:22px 24px;border-radius:18px;background:#fff;border:1px solid var(--line-soft);
}
.sc h3{font-size:17px}
.sc p{margin:0;color:var(--ink-2);font-size:15px}

.steps{
  list-style:none;margin:42px 0 0;padding:0;
  display:grid;grid-template-columns:repeat(3,1fr);gap:18px;
}
.steps li{
  background:#fff;border:1px solid var(--line-soft);border-radius:20px;padding:28px 24px;
}
.step-n{
  font-size:13px;font-weight:700;letter-spacing:.12em;color:var(--accent);
  margin-bottom:14px;
}
.steps h3{font-size:20px;margin-bottom:10px}
.steps p{margin:0;color:var(--ink-2);font-size:15px}

/* CTA */
.cta{
  padding:100px 0 110px;
  background:
    radial-gradient(800px 300px at 50% 0%, rgba(16,163,127,.18), transparent 70%),
    #0d0d0d;
  color:#fff;text-align:center;
}
.cta h2{font-size:clamp(28px, 4vw, 42px);max-width:16em;margin:0 auto}
.cta p{margin:16px 0 28px;color:rgba(255,255,255,.65);font-size:17px}
.btn-light{
  display:inline-flex;align-items:center;justify-content:center;
  padding:14px 28px;font-size:16px;font-weight:650;
  background:#fff;color:#111;border-radius:999px;
}
.btn-light:hover{transform:translateY(-1px)}

/* footer */
.footer{
  border-top:1px solid var(--line-soft);
  padding:36px 0 48px;background:#fff;
}
.footer-in{
  display:flex;flex-wrap:wrap;gap:16px;align-items:center;justify-content:space-between;
}
.footer-brand{display:flex;align-items:center;gap:10px;font-weight:650}
.footer nav{display:flex;gap:18px;flex-wrap:wrap}
.footer nav a{font-size:14px;color:var(--ink-2);font-weight:500}
.footer nav a:hover{color:var(--ink)}
.footer .tiny{width:100%;color:var(--ink-3);margin:0}

/* responsive */
@media (max-width:900px){
  .nav-links{display:none}
  .nav-cta .btn-ghost{display:none}
  .nav-burger{display:block;margin-left:auto}
  .nav-in{gap:12px}
  .mock-body{grid-template-columns:1fr}
  .mock-side{display:none}
  .mock-cards{grid-template-columns:1fr}
  .duo,.grid-3,.lib,.steps{grid-template-columns:1fr}
  .sc{grid-template-columns:1fr;gap:8px}
  .section{padding:72px 0}
  .hero{padding-top:48px}
}
@media (max-width:520px){
  .wrap{width:100% - 32px;width:calc(100% - 32px)}
  .hero h1{letter-spacing:-.04em}
  .hero-actions .btn-primary,
  .hero-actions .btn-line{width:100%}
}